BIOLOGY 
•  II  RAK1 

8 


All  figures  after  Castle 

f  PLATE,  IV,  .QV^RJAJT  TRANSPLANTATION 

Fig.  1.  A  youn}*/bl»ck  guin$a,'pig  iSjfeltlje  one  whose  ovaries  were  transplanted  into  the 
albino  shown  «in*fi*ig.  2.  tig!  2.  An  afbino*  gnjnea-pig  whose  ovaries  were  replaced  by 
those  from  su^h  a^uinea-pigf  aatfiat  »hoWfn  in  ^*g.  1.  Fig.  3.  An  albino  male  guinea-pig 
with  which  tti«  QI{B  eh$wn  m  Fj&  2  was «a»ated;  /Figs.  4  and  5.  Two  of  the  six  offspring 
of  the  r»afciogs»o*f  the  g\ifritea-pigs*sn6wn  in  Figs.  2  and  3.  All  the  offspring  were  black. 


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1914 

BIOLOGY  AND   SOCIAL 
PROBLEMS 

BY 

GEORGE  HOWARD  PARKER,  S.D. 

PROFESSOR  OF  ZOOLOGY  IN  HARVARD  UNIVERSITY 

AND  WILLIAM  BREWSTER  CLARK  LECTURER 

AT  AMHERST  COLLEGE  FOR  1914 


BOSTON  AND  NEW  YORK 
HOUGHTON  MIFFLIN  COMPANY 


1914 


BIOLOGY 


COPYRIGHT,  1914,  BY  GEORGE  HOWARD  PARKER 
ALL  RIGHTS  RESERVED 

Published  November  1914. 


TO 

L.  M.  P. 


FOREWORD 

THE  unique  characteristic  of  modern  times 
—  one  which  gives  every  indication  of  being 
permanent  —  is  that  the  world,  both  personal 
and  external,  is  to  an  apparently  increasing 
degree  in  a  state  of  change.  The  immense 
significance  of  this  fact  is  as  yet  but  dimly 
perceived.  The  new  modifies  the  old  or  dis- 
places it  in  every  department  of  life  without 
exception  and  with  increasing  rapidity.  New 
ideas,  new  movements,  new  ways  of  looking 
at  things  present  themselves  for  attention  for 
the  first  time  or  call  upon  people  to  change 
their  attitude  towards  things  they  had  con- 
sidered settled.  This  state  of  the  world  ren- 
ders the  practical  problems  of  personal  con- 
duct and  social  policy  increasingly  vital  and 
complex,  and  makes  the  task  of  a  college  in 
its  relation  to  them  as  much  more  difficult  as 
an  institution  is  less  mobile  than  an  indi- 
vidual. 

To  assist  Amherst  College,  therefore,  in 
throwing  light  in  a  genuinely  scientific  spirit 
upon  the  relation  of  the  research,  discovery, 


viii  FOREWORD 

and  thought  of  the  day  to  individual  attitude 
and  social  policy  is  our  aim  in  the  founda- 
tion of  these  lectures.  Such  light  may  come 
through  a  recent  discovery  in  natural  or  ap- 
plied science,  through  a  new  tendency  in  art, 
literature,  or  music;  it  may  be  the  result  of 
some  painstaking  research  in  history  or  an- 
thropology ;  or  it  may  be  found  in  some  vital 
movement,  religious,  philosophic,  economic,  or 
political.  It  is  our  wish  that  men  and  women 
who  are  in  the  position  of  leaders  in  such 
phases  of  the  life  of  the  day  shall  give  to 
Amherst  College  and  the  world  an  exposition 
of  their  particular  work  in  its  relation  to  what 
they  conceive  to  be  a  modern  outlook. 

We  give  these  lectures  in  memory  of  Wil- 
liam Brewster  Clark,  M.D.,  who  graduated 
from  Amherst  in  the  class  of  1876.  We  be- 
lieve that  no  place  for  a  memorial  to  him 
could  be  more  fitting  than  the  college  which 
he  loved  with  a  devotion  characteristically 
rich  and  sincere,  nor  any  form  more  suitable 
than  lectures  on  subjects  which  to  him  would 
be  most  absorbing. 

FANNY  H.  CLARK, 
W.  EVANS  CLAKK. 

NEW  YORK  CITY,  11  March,  1913. 


POSTSCRIPT 

SINCE  the  publication  of  the  first  series  of 
lectures  it  has  seemed  advisable  to  limit  the 
scope  of  future  series  more  definitely.  Should 
the  field  of  subjects  include  all  of  those  which 
affect  "individual  attitude  and  social  policy," 
it  would  make  for  a  loss  of  coherence  and 
continuity  in  the  lectures  as  a  whole.  Accord- 
ingly, we  have  decided  to  confine  the  subjects, 
for  the  present  at  least,  to  those  which  bear 
directly  upon  a  most  important  phase  of  the 
general  problem  of  "  social  policy  "  —  that  of 
Social  Control. 

The  idea  of  unlimited  human  progress  is 
but  four  centuries  old.  The  idea  of  the  con- 
scious direction  of  that  progress  is  yet  in  its 
infancy.  Few  indeed  there  are  who  do  not 
still  consider  human  characteristics,  institu- 
tions, and  environment  to  be  as  immutably 
fixed  as  the  hills  and  the  ocean.  The  merest 
scattering  of  human  beings  realizes  that  with 
knowledge  and  cooperative  effort  large  masses 
of  people  can,  in  great  measure,  seize  their 
destiny  and  mold  it  to  their  conscious  aims. 

With  the  birth  of  this  idea  of  Social  Con- 
trol among  the  few  have  come  large  plans  of 


x  POSTSCRIPT 

social  reorganization  and  improvement  to 
affect  the  many.  The  salient  feature  of  most 
of  these  plans,  however,  is  their  speculative 
and  dogmatic  quality.  They  lack,  quite  nat- 
urally, the  basis  of  positive  knowledge  and 
experience.  Social  Control  to-day  is  more 
prophecy  than  science. 

It  is  our  hope,  therefore,  that  in  these  lec- 
tures we  may  contribute  toward  this  new  sci- 
ence by  providing  a  forum  for  those  who  have 
data  relating  to  the  problem. 

With  this  limitation  of  their  scope  the  lec- 
tures will  be  continued  along  the  lines  origin- 
ally planned. 

F.  H.  e. 

W.  E.  C. 

ARDNAMURCHAN 

LOWER  ARGYLE,  N.S. 

12  August,  1914. 


CONTENTS 

INTRODUCTION xv 

I.  THE  NERVOUS  SYSTEM 1 

II.  HORMONES 39 

III.  KEPRODUCTION     ."• 63 

IV.  EVOLUTION  .  98 


ILLUSTRATIONS 

OVARIAN  TRANSPLANTATION   (Plate  IV) 

(p.  Ill)     .     .     .     .     ...     .     Frontispiece 

From  photographs  in  the  possession  of  Professor 
W.  E.  Castle. 

FEMINIZED  GUINEA-PIGS  (Plate  I)      ...    52 

By  courtesy  of  Professor  E.  Steinach. 

MENDELIAN  INHERITANCE  (Plate  II)  .    .    .    86 

From  photographs  in  the  possession  of  Professor 
W.  E.  Castle. 

UNIT  CHARACTERS  (Plate  III)  .     .'..  ...     92 
From  photographs  in  the  possession  of  Professor 
W.  E.  Castle. 


INTRODUCTION 

IN  our  endeavor  to  better  the  conditions  of 
man,  probably  no  facts  are  more  worthy  of 
consideration  than  those  included  in  his  natu- 
ral history,  a  science  which  in  its  wider  aspects 
has  done  more  in  the  last  few  centuries  than 
any  other  body  of  knowledge  to  change  our 
opinion  of  man's  real  nature  and  of  his  place 
in  the  world.  How  great  this  change  has  been 
will  be  evident  if  we  compare  the  ancient  view 
of  man's  relation  to  the  universe  with  the 
opinions  of  to-day.  In  early  times  the  heavens 
were  supposed  to  be  a  dome  from  which  show- 
ers descended  upon  the  expanse  of  earth  be- 
neath, fertilizing  it  and  rendering  it  a  fit  abode 
for  man.  Here  he  built  habitations,  cultivated 
the  soil,  and  peopled  the  earth  with  his  off- 
spring. To  him  the  earth  seemed  the  center 
of  the  universe,  and  he  believed  that  its  crea- 
tion was  for  his  convenience  and  welfare. 

But  this  anthropocentric  conception  was 
not  without  its  difficulties.  Even  as  early  as 
the  days  of  Aristotle,  good  reasons  were  given 
for  the  belief  that  the  earth  was  not  a  plain 


xvi  INTRODUCTION 

under  the  vaulted  heavens,  but  a  globe.  This 
conclusion  was  accepted  by  many  of  the  early 
astronomers,  and  much  speculation  was  pro- 
voked by  it  as  to  the  condition  of  the  antip- 
odes and  the  relation  of  the  earth  to  the 
heavenly  bodies.  In  the  system  devised  by 
Ptolemy  in  the  early  part  of  our  era,  the  earth 
was  placed  at  the  center  of  things  and  the 
heavenly  bodies  were  supposed  to  move  around 
it.  This  geocentric  theory  was  for  a  long  time 
the  prevailing  opinion  of  the  structure  of  the 
universe.  It  permeated  much  of  the  Middle 
Ages  and  afforded  the  physical  setting  for 
such  great  works  of  art  as  the  Divine  Comedy. 
It  was,  however,  eventually  replaced  by  the 
Copernican  theory,  according  to  which  the 
sun,  not  the  earth,  is  the  central  body  around 
which  the  others  move.  So  completely  does 
this  heliocentric  theory  meet  the  facts  of  as- 
tronomy that  its  truth  is  beyond  dispute.  But 
in  abandoning  the  old  for  the  new,  man  was 
obliged  to  give  up  his  idea  of  a  centrally  lo- 
cated habitation.  In  fact  it  may  be  said  that 
the  Copernican  theory  removed  the  last  physi- 
cal vestige  of  the  support  for  the  anthropo- 
centric  conception  and  left  this  idea  to  survive 
merely  as  a  poetic  figure. 


INTRODUCTION  xvii 

But  modern  astronomy  has  done  vastly 
more  than  displace  the  habitation  of  man  from 
an  assumed  central  position.  It  has  given  us 
a  view  of  the  structure  of  the  universe  such 
as  was  never  dreamed  of  before.  Not  only  is 
the  earth  one  of  the  smaller  members  of  an 
association  of  heavenly  bodies  traveling  at 
enormous  speed  around  a  centrally  located 
sun,  but  the  whole  solar  system  thus  consti- 
tuted, though  its  diameter  is  between  five  and 
six  thousand  millions  of  miles,  is  small  com- 
pared with  even  the  measurable  space  beyond 
it.  The  star  nearest  to  us  is  alpha  centauri, 
distant  between  four  and  five  thousand  times 
the  diameter  of  our  system.  Light  from  this 
star  takes  over  four  years  to  reach  us.  No 
means  are  known  for  measuring  the  distances 
of  the  most  remote  stars.  Some  of  them  have 
been  estimated  to  be  from  seven  to  eight  thou- 
sand light-years  from  us ;  that  many  of  them 
are  removed  by  more  than  one  hundred  light- 
years  is  certain.  This  distance  amounts  to 
over  one  hundred  thousand  times  the  diame- 
ter of  our  solar  system  and  is  unquestionably 
far  short  of  the  actual  distances  of  many  stars. 
None  of  us  in  this  audience  will  live  to  see  the 
light  which  at  this  moment  is  starting  toward 


xviii  INTRODUCTION 

the  earth  from  many  of  these  bodies.  Such 
expanses  of  space  as  are  implied  in  these  meas- 
urements were  probably  never  imagined  by 
even  the  astronomers  of  olden  times  and  cer- 
tainly never  by  those  who  held  the  ancient 
opinion  of  a  flat  earth  vaulted  by  the  heavens. 
The  immensity  of  these  stretches  in  relation 
to  the  earth  and  to  man  brings  us  to  a  realiza- 
tion of  our  own  insignificance.  Man  is  as  the 
merest  atom  among  these  magnitudes;  and 
the  nations  "  are  counted  as  the  small  dust 
of  the  balance." 

If,  then,  the  human  race  can  no  longer  claim 
the  central  place  in  the  universe,  is  not  the 
observed  of  all  observers,  what  can  be  said  of 
it?  To  this  question  natural  science  has  re- 
plied that  man  is  the  product  of  his  immedi- 
ate environment.  And  it  therefore  behooves 
those  who  have  his  welfare  at  heart  to  ac- 
quaint themselves  with  this  environment  as 
well  as  with  man  regarded  as  one  of  its  prod- 
ucts. It  is  the  object  of  these  lectures  to  at- 
tempt to  sketch  in  outline  something  of  man's 
nature  from  this  standpoint. 

Viewed  near  at  hand  and  as  a  part  of  his  im- 
mediate surroundings,  man  has  a  twofold  in- 
terest. He  is,  first  of  all,  an  incessantly  re- 


INTRODUCTION  xix 

sponsive  organism  performing  an  enormous 
variety  of  complicated  and  intricate  acts  some 
of  which  are  indicative  of  the  highest  order 
of  intelligence;  and,  secondly,  he  possesses 
powers  of  reproduction  in  that  he  can  leave 
behind  him  offspring  who,  while  they  carry 
with  them  the  vast  inheritance  of  the  race,  < 
are  also  the  means  of  that  gradual  change  / 
which  has  made  his  own  coming  possible.  In  ) 
dealing  with  the  natural  history  of  man  in  • 
the  following  lectures  these  two  aspects  of  his 
nature  will  be  the  chief  topics  for  consider* 
ation. 


1    ' 


BIOLOGY  AND  SOCIAL 
PROBLEMS 


THE  NEKVOUS  SYSTEM 

OF  the  sixteen  hundred  millions  of  human 
beings  that  populate  the  earth  to-day  expe- 
rience has  shown  us  that  we  usually  have  no 
difficulty  in  learning  to  distinguish  one  from 
another  with  perfect  certainty.  Physical  traits, 
such  as  stature,  color  of  hair  or  eyes,  facial 
form  and  proportions,  are  the  elements  usually 
employed  in  this  discrimination ;  but  only  a 
finger  print  may  suffice.  When,  however,  we 
ask  ourselves  what  constitutes  the  real  in- 
dividual whom  we  have  learned  to  know,  we 
are  less  inclined  to  dwell  on  physical  traits 
than  on  the  innumerable  characteristic  move- 
ments in  the  form  of  common  acts,  responses, 
and  replies  which  are  habitual  with  him  and 
which  we  believe  to  indicate  in  him  certain 
mental  states  and  attitudes  that  we  have  come 
to  associate  with  him  as  part  of  his  nature. 


$;/;  BIOLOGY  AND  .SOCIAL  PROBLEMS 

These  traits  seem  to  us  to  indicate  the  real  in- 
dividual more  truly  than  such  obvious  physi- 
cal peculiarities  as  stature,  color  of  hair,  and 
the  like,  for  the  reason  probably  that  expe- 
rience has  taught  us  that,  though  the  physi- 
cal traits  may  change  with  time,  the  others 
remain  relatively  stable  and  may  be  counted 
upon  as  more  or  less  permanently  present. 
We  group  these  relatively  stable  traits  under 
the  head  of  personality,  and  we  think  of 
these  collectively  as  constituting  the  core  and 
essence  of  the  individual,  the  real  and  effec- 
tive part  under  cover  of  the  more  obviously 
physical,  the  ego  or  soul  of  the  situation.  It 
is  the  possession  of  a  centralized  nature,  of 
an  active  personality,  that  makes  each  normal 
human  being  an  effective  and  responsible  unit 
in  society.  His  attitudes  are  the  result  of  this 
possession ;  his  acts  are  determined  by  it ;  it  is 
in  fact  his  inmost  self. 

What  can  be  said  about  personality  so  far 
as  its  natural  history  is  concerned?  How  is  it, 
for  instance,  related  to  the  body?  Many  of  the 
ancients  believed  personality  to  permeate  more 
or  less  completely  the  whole  human  frame ;  it 
was  a  shade  or  shadow  that  simulated  the  form 
of  the  material  body  in  all  its  details,  but  was 


THE  NERVOUS  SYSTEM  3 

airy  in  its  lightness  and  transparency,  and, 
like  a  shadow,  it  might  separate  itself  some- 
what from  the  body.  More  accustomed  to 
think  of  an  animal  as  a  whole  than  as  an  as- 
semblage of  parts,  they  were  prone  to  conceive 
of  functions  as  more  or  less  diffusely  related 
to  the  body.  Yet  that  a  certain  degree  of  local- 
ization was  admitted  is  seen  in  the  opinion 
ascribed  to  Galen  that  the  brain  is  the  seat 
of  the  rational  soul,  the  heart  the  location  of 
courage  and  fear,  and  the  liver  that  of  love. 
This  localization  became  more  or  less  restricted 
in  later  times.  Thus,  Vesalius  taught,  in  the 
sixteenth  century,  that  the  chief  soul  was  en- 
gendered in  the  brain  by  virtue  of  the  powers 
of  the  proper  material  and  form  of  that  organ. 
And,  although  Stahl  attempted,  a  century  and 
a  half  later,  to  revive  the  belief  that  the  soul 
and  the  sensorium  commune  were  diffused  over 
the  whole  body,  that  is,  were  resident  as  well 
in  the  tip  of  the  finger  as  in  the  brain,  the  idea 
of  the  localization  of  these  active  properties 
in  the  nervous  system  became  so  well  grounded 
through  the  investigations  of  the  physicians  of 
that  time,  particularly  Haller,  as  to  assume  the 
form  of  permanency.  This  growth  of  knowl- 
edge led  directly  to  the  modern  view  that 


4        BIOLOGY  AND  SOCIAL  PROBLEMS 

personality  is,  strictly  speaking,  a  property  of 
the  nervous  system  and  is  in  no  true  sense  the 
direct  result  of  any  other  system  of  organs. 
The  nervous  system,  to  be  sure,  is  embedded 
among  other  organs  of  the  body,  and  the 
environment  thus  provided  influences  pro- 
foundly its  condition  and  action;  but  what  is 
meant  by  individual  personality,  acuteness  or 
dullness  of  sense,  quickness  or  slowness  of 
action,  temperamental  traits,  such  as  a  gloomy 
or  bright  disposition,  incapacity,  shiftless- 
ness,  honesty,  thriftiness,  or  sweetness,  are  all, 
strictly  speaking,  functions  of  the  nervous 
system.  All  these  traits,  then,  that  count  for 
so  much  in  making  the  individual  an  effec- 
tive or  ineffective  member  of  society,  are  the 
direct  product  of  his  nervous  system,  a  system 
which  is  equaled  in  its  importance  in  social 
problems  only  by  the  reproductive  system. 

How  the  nervous  system  subserves  person- 
ality, and  how  in  man  it  has  come  to  be  the 
seat  of  that  general  function,  are  questions 
whose  solutions  are  to  be  sought  in  the  condi- 
tions of  our  nervous  organs  to-day  and  in  the 
course  which  their  evolution  has  taken. 

The  body  of  man,  like  that  of  other  higher 
animals,  is  composed  of  an  immense  aggre- 


THE  NERVOUS  SYSTEM  '  5 

gation  of  cells,  such  as  skin  cells,  bone 
cells,  muscle  cells,  gland  cells,  and  so  forth, 
arranged  so  as  to  constitute  its  organs.  The 
nervous  system  in  the  higher  animals,  like  their 
other  sets  of  organs,  is  also  composed  of  cells, 
but  nerve  cells  are  very  unlike  other  cells. 
Although  the  analysis  of  the  body  from  this 
standpoint  was  undertaken  three  quarters  of  a 
century  ago,  the  unique  character  of  the  nerve 
cell  was  only  first  fully  grasped  by  Waldeyer 
in  1891.  Each  nerve  cell,  or  neurone,  as  Wal- 
deyer designated  it,  consists  of  a  nucleated  cell 
body,  the  so-called  ganglion  cell  of  the  older 
neurologists,  from  which  extremely  attenuated 
processes,  the  nerve  fibers,  reach  out  to  the 
most  distant  parts  of  the  animal.  These  proc- 
esses, which  for  a  long  time  were  not  recog- 
nized as  belonging  to  the  nerve  cell,  are  the 
most  characteristic  parts  of  its  structure.  Ex- 
tending as  they  do  in  the  larger  animals  for  even 
some  meters  from  their  cell  bodies,  they  afford 
an  example  of  the  special  extension  of  a  single 
cell  such  as  is  seen  in  no  other  histological 
element.  In  man,  for  instance,  neurone  proc- 
esses are  known  to  begin  in  the  middle  of  the 
back  and  extend  to  the  toes,  a  distance  well 
over  a  meter.  Although  the  human  body  con- 


6        BIOLOGY  AND  SOCIAL  PROBLEMS 

tains  other  elongated  organs  than  nerves,  as, 
for  example,  muscles  and,  particularly,  blood 
vessels,  the  cells  of  these  parts  are  in  no  wise 
elongated  as  the  cells  of  the  nervous  system 
are.  In  this  respect  the  nervous  system  seems 
to  be  unique. 

Described  from  the  standpoint  of  the  histo- 
logical  elements  composing  it,  the  nervous 
system  of  man  and  the  other  higher  animals 
may  be  said  to  be  made  up  of  an  enormously 
intricate  system  of  interwoven  neurones.  The 
number  of  these  elements  in  such  a  nervous 
system  is  incredibly  great  and  certainly  reaches 
many,  many  millions.  The  complexity  of  their 
arrangement  is  familiar  to  every  reader  of 
textbooks  on  neurology,  but  even  the  most 
involved  descriptions  in  the  texts  are  as  sim- 
plicity itself  compared  with  the  real  complex- 
ity in  such  a  nervous  system  as  that  of  any  of 
the  higher  animals,  not  to  mention  man. 

Yet,  notwithstanding  the  enormous  com- 
plexity in  the  arrangement  of  the  neurones  in 
such  animals,  these  elements  are  capable  of  a 
relatively  simple  classification.  A  large  num- 
ber of  them  extend  from  the  skin  and  the  or- 
gans of  special  sense,  such  as  the  nose,  the 
tongue,  the  ear,  and  the  like,  to  the  central 


THE  NERVOUS  SYSTEM  7 

nervous  organs.  These  neurones  become  ac- 
tive when  their  sense  organs  are  appropriately 
stimulated  and  transmit  impulses  from  the 
periphery  to  the  central  organs.  They  are, 
therefore,  classed  as  afferent  or  sensory  neu- 
rones. Another  set  of  neurones  transmit  im- 
pulses from  the  central  organs  to  the  muscles 
and  other  mechanisms  of  response.  These  are 
called  efferent  neurones.  It  might  seem  that 
the  afferent  neurones  leading  into  the  central 
organs  and  the  efferent  neurones  leading  out 
from  them  were  all  that  were  necessary  for 
even  a  complex  nervous  system,  but  as  a  mat- 
ter of  fact  there  is  a  host  of  other  neurones 
which  never  reach  beyond  the  limits  of  the 
central  nervous  system  and  which  are  con- 
cerned with  bringing  one  part  of  this  system 
into  communication  with  another.  As  a  rule 
these  neurones  cannot  be  designated  appro- 
priately as  either  afferent  or  efferent.  They 
have,  therefore,  been  termed  internuncial.  In 
the  higher  animals  they  certainly  far  outnum- 
ber the  afferent  and  the  efferent  elements  col- 
lectively and  constitute  the  bulk  of  the  central 
nervous  system  in  these  forms.  Thus,  not- 
withstanding the  enormous  numbers  of  neu- 

C5 

rones  in  the  higher  animals  and  the  intricacy 


8         BIOLOGY  AND  SOCIAL  PROBLEMS 

and  complexity  of  their  arrangement,  they 
can  be  grouped  conveniently  under  the  three 
classes,  afferent,  efferent,  and  internuncial. 

The  general  arrangement  of  the  neurones 
in  any  complex  nervous  system,  as  indicated 
in  the  preceding  classification,  foreshadows  in 
a  way  the  simplest  complete  nervous  act,  the 
reflex.  When  an  animal  is  stimulated,  it  usu- 
ally responds  almost  immediately  by  a  move- 
ment. In  most  animals  this  operation  is  carried 
out  by  the  nervous  system  and  the  appended 
motor  organs,  the  muscles.  Such  a  simple 
neuromuscular  operation  is  called  a  reflex.  It 
involves  the  stimulation  and  activity  of  an 
afferent  neurone,  whereby  a  nervous  impulse 
is  sent  into  the  central  organ  from  which  issues 
over  an  efferent  neurone  a  motor  impulse  that 
brings  a  muscle  or  a  group  of  muscles  into 
play.  Such  an  action  can  be  conceived  to  be 
restricted  to  the  two  classes  of  neurones  men- 
tioned, namely,  the  afferent  and  the  efferent, 
but  probably  in  the  great  majority  of  actual 
occurrences  internuncial  neurones  are  included, 
and  these  strictly  central  elements  mediate  be- 
tween the  central  ends  of  the  efferent  and  of 
the  afferent  neurones.  The  reflex  is  thus  a 
physiological  unit,  so  to  speak,  in  the  action 


THE  NERVOUS  SYSTEM  9 

of  the  nervous  system,  and  though  it  can 
scarcely  be  said  to  exist  in  the  bald  way  in 
which  it  has  just  been  described,  the  idea  of 
the  reflex  has  been  certainly  a  most  important 
conception  in  the  analysis  of  nervous  opera- 
tions. 

Many  of  the  elemental  movements  which 
the  body  of  man  is  continually  exhibiting  par- 
take of  the  nature  of  reflexes,  and  if  we  ex- 
tend this  term  to  include  operations  which  in- 
volve consciousness,  and  there  seems  to  be  no 
good  reason  why  we  should  not  so  extend  it, 
almost  every  form  of  nervous  activity  may  be 
classed  under  it.  Many  of  our  daily  acts  are 
reflexes  of  the  simplest  possible  kind ;  our  in- 
stinctive movements  and  our  habits  are  groups 
of  these  reflexes  more  or  less  complex  in  their 
associations  and  in  their  sequences.  In  fact 
the  ensemble  of  nervous  activity  that  we  rec- 
ognize in  personality  rests  on  a  background 
of  reflex  operation  and  is  itself  made  up  in 
large  part  of  just  this  mode  of  action.  Let  us 
turn  now  to  a  consideration  of  some  of  the 
chief  classes  of  nervous  activity  in  man,  that 
we  may  see  something  of  their  significance  to 
him  as  a  social  organism. 
.  If  at  the  outset  we  attempt  to  discover 


10       BIOLOGY  AND  SOCIAL  PROBLEMS, 

those  reflex  operations  of  our  bodies  which 
seem  to  us  to  exhibit  the  most  primitive  forms 
of  activity,  we  may  well  turn  to  the  responses 
of  our  internal  organs.  The  heart  of  a  normal 
adult  man  in  repose  beats  at  a  rate  of  about 
seventy  pulses  per  minute.  If  he  rises  and 
stands,  it  usually  increases  its  beats  to  about 
eighty  per  minute;  if  he  lies  down,  the  rate 
may  fall  to  some  sixty  per  minute.  Unusual 
exercise,  as  in  running  and  other  forms  of 
vigorous  muscular  work,  calls  forth  a  marked 
increase  in  the  rate  which  may  last  for  some 
time  after  the  exercise  has  ceased.  All  these 
changes  in  the  action  of  the  heart  are  con- 
cerned with  the  appropriate  supply  of  blood 
to  the  working  body,  particularly  its  muscles, 
and  are  of  an  obviously  adaptive  kind.  Since 
they  follow  with  great  precision  and  regular- 
ity the  changes  in  the  state  of  the  individual, 
they  might  be  looked  upon  as  good  examples 
of  simple  reflexes.  But  a  careful  inspection 
of  them  will  show  that  this  is  not  strictly 
true. 

The  heart  of  man,  like  that  of  other  higher 
animals,  receives  at  least  two  kinds  of  nerve 
fibers,  sympathetic  and  vagus  fibers.  The 
first  of  these  on  stimulation  accelerates  the 


THE  NERVOUS  SYSTEM  11 

heart-beat;  the  second  retards  it  and  may 
even  bring  it  to  a  complete  standstill.  Such 
a  control  of  a  muscle  is  by  no  means  usual 
and  suggests  at  once  that  the  heart  must 
be  an  exceptional  organ.  But  what  is  of  still 
more  significance  than  this  peculiar  form  of 
control  is  the  fact  that  the  heart  will  keep  on 
beating  for  many  hours  after  all  its  nervous, 
connections  with  the  rest  of  the  body  have  been 
severed.  This  condition  would  be  very  difficult 
to  explain  from  the  usual  standpoint  of  the 
relation  of  nerve  to  muscle,  were  it  not  known, 
from  the  time  of  Remak,  over  half  a  century 
ago,  that  the  heart  muscle  is  permeated  with  a 
network  of  nerve  cells  and  thus  may  be  said 
to  carry  its  own  nervous  mechanism  within  it- 
self. Hence  it  is  clear  that  the  sympathetic  and 
vagus  nerves  are  not  related  to  the  heart  mus- 
cle as  ordinary  motor  nerves  are  to  the  muscles 
that  they  control,  but  are  to  be  regarded  as  an 
auxiliary  nervous  apparatus  superimposed  on 
the  heart  whose  true  nervous  mechanism  may 
be  within  its  own  substance. 

It  is  not  my  purpose  to  enter  here  into  the 
vexed  question  of  the  nature  of  the  heart-beat 
in  the  adult  vertebrate.  As  you  are  probably 
aware,  this  question  has  divided  physiologists 


12       BIOLOGY  AND  SOCIAL  PROBLEMS 

into  two  opposing  camps,  the  neurogenists 
who  believe  that  the  heart-beat  is  essentially 
nervous  in  its  origin  and  the  myogenists  who 
hold  that  it  is  muscular  in  source.  But  quite 
aside  from  the  way  in  which  this  question 
may  be  settled,  one  point  seems  to  be  well  es- 
tablished, and  that  is  that  in  the  embryo  of 
such  a  vertebrate  as  the  chick,  the  heart  be- 
gins to  beat  before  any  nervous  tissue  what- 
ever can  be  discovered  in  it.  At  this  stage, 
then,  the  heart-beat  must  be  purely  muscular 
and  the  nervous  complications  such  as  they 
are  in  the  adult  must  be  of  later  origin. 

The  peculiar  condition  seen  in  the  embry- 
onic heart  suggests  that  in  primitive  animals 
muscle  may  have  preceded  nerve  in  its  evo- 
lution, and  in  fact  confirmation  of  this  view 
seems  to  be  presented  by  sponges.  In  these 
animals  the  presence  of  muscular  tissue  was 
long  ago  recognized,  and  recent  studies  on 
their  activities  have  shown  that  sponges  are 
enabled  by  means  of  this  tissue  to  close  their 
pores  and  other  apertures,  and  change  slightly 
the  form  of  their  bodies.  They  are  not  known 
to  possess  any  nervous  tissues  whatever,  and 
the  responses  which  they  exhibit,  like  those 
of  the  embryonic  vertebrate  heart,  are  appar- 


THE  NERVOUS  SYSTEM  13 

ently  dependent  entirely  upon  the  direct  stim- 
ulation of  muscle. 

In  the  adult  human  body  there  is  at  least 
one  muscle  which,  like  the  embryonic  heart, 
is  open  normally  to  a  certain  degree  of  direct 
stimulation.  This  is  the  sphincter  pupillae  by 
means  of  which  the  pupil  of  the  eye  is  con- 
stricted. This  muscle  is  ordinarily  under  the 
control  of  the  oculomotor  nerve,  and  it  re- 
sponds reflexly  by  contracting  when  the  ret- 
ina is  brightly  illuminated.  But  it  can  also 
be  made  to  contract  by  direct  stimulation.  If, 
in  a  blind  person,  a  strong  beam  of  light  is 
thrown  through  the  pupil  on  to  the  retina, 
but  without  illuminating  the  iris,  the  muscle 
does  not  shorten,  thus  showing  that  the  or- 
dinary reflex  arc  is  inoperative.  If,  now,  the 
same  beam  is  directed  against  the  iris,  in 
which  the  muscle  is  embedded,  a  contraction 
follows,  thus  giving  evidence  of  the  direct 
stimulation  of  the  muscle.  Certain  parts  of  N 
the  musculature  of  our  bodies,  then,  exhibit 
forms  of  response  that  are  more  primitive  than 
the  reflex  and  that  indicate  something  of  the 
probable  nature  of  the  beginnings  of  neuro- 
muscular  activity. 

If  the  embryonic  vertebrate  heart  illustrates 


14       BIOLOGY  AND  SOCIAL  PROBLEMS 

a  stage  in  the  evolution  of  neuromuscular 
mechanisms  at  which  no  reflex  can  occur,  the 
adult  organ  shows,  in  certain  relations  at  least, 
a  simple  form  of  true  reflex.  The  heart  of  the 
rabbit  is  invaded  by  a  small  nerve  which  arises 
as  a  branch  from  the  vagus  and  which  has 
been  called  the  depressor  nerve  of  the  heart. 
If  this  nerve  is  cut  and  its  peripheral  end  is 
stimulated,  no  result  follows,  thus  showing 
that  the  nerve  has  no  motor  relations  with 
the  heart.  If,  on  the  other  hand,  the  central 
end  is  stimulated,  a  general  fall  in  blood  pres- 
sure follows,  demonstrating  that  this  nerve 
is  an  afferent  nerve  whose  activity  induces 
through  the  central  nervous  system  an  en- 
largement of  the  blood  vessels  of  the  body. 
The  receptor  endings  for  this  nerve  are  in 
large  part  in  the  heart  and  are  stimulated  by 
each  stroke  of  that  organ.  When,  therefore, 
the  action  of  the  heart  is  vigorous  the  effect 
on  the  endings  of  the  depressor  nerve  is  such 
as  to  call  forth  a  general  enlargement  of  the 
blood  vessels  of  the  body,  thus  providing  the 
heart,  in  a  simple  reflex  way,  with  an  ample 
outlet  for  the  blood.  Since  this  adjustment 
goes  on  quite  without  our  knowledge,  it  is 
correctly  described  as  a  reflex  unassociated 


I 

THE  NERVOUS  SYSTEM  15 

with  consciousness,  and  in  this  respect  is  like 
other  deep-seated  reflexes  such  as  those  by 
which  the  food  is  moved  through  the  digestive 
tube.  Operations  of  this  kind  constitute,  per- 
haps, the  most  primitive  class  of  reflex  move- 
ments with  which  we  are  acquainted.  Al- 
though they  may  be  absolutely  unassociated 
with  consciousness,  they  exhibit  a  nicety  of 
adjustment  that  is  most  baffling  when  explan- 
ation is  attempted,  for  they  show  every  appear- 
ance of  intelligent  control.  They,  therefore, 
afford  evidence  for  that  conception  of  the  or- 
ganism which  has  recently  been  so  vigorously 
advanced  by  the  neovitalists,  namely,  that 
the  organism  continually  exhibits  conditions 
which,  when  we  attempt  to  explain  them,  seem 
to  necessitate  the  assumption  of  an  element  of 
intelligence. 

The  class  of  reflexes  just  mentioned,  that 
is,  those  unassociated  with  consciousness,  make 
up  in  all  probability  the  large  part  if  not  the 
whole  of  the  nervous  life  of  many  of  the  lower 
animals.  While  such  a  statement  can  be  at  best 
only  a  judgment  without  the  possibility  of 
final  proof,  it  seems  more  probable  that  the 
nervous  life  of  sea  anemones,  jelly  fishes,  and 
other  lowly  organized  forms  is  made  up  of  sim- 


16       BIOLOGY  AND  SOCIAL  PROBLEMS 

pie  nervous  acts  like  the  one  just  described  than 
that  these  animals  have  any  real  conscious  ex- 
istence. They  are  probably  much  more  correctly 
described  as  animal  automata  than  as  beings 
possessing  even  a  low  degree  of  intelligence. 
Many  reflexes  of  the  human  body  take  place 
with  the  certainty  and  precision  of  those  just 
discribed,  but,  unlike  them,  are  associated 
with  consciousness.  If  we  irritate  the  surface 
of  the  eye  by  touching  it,  we  involuntarily 
wink.  Here,  then,  is  a  simple  reflex  which  is 
associated  with  an  irritating  sensation,  though 
the  response  itself  is  involuntary.  Sneezing 
and  coughing  are  similar  reflexes.  If  we  re- 
peatedly strike  a  dog  on  one  side  of  the  mid- 
dle of  the  back,  he  will  begin  scratching  move- 
ments with  the  hind  leg  of  that  side.  Not  only 
are  muscles  thus  reflexly  brought  into  action, 
but  glands  also  serve  as  the  efferent  organs  for 
such  reflex  activity.  When  the  surface  of  the 
eye  is  irritated,  not  only  does  the  lid  move, 
but  the  eye  waters,  that  is,  there  is  a  reflex  oper- 
ation of  the  lachrymal  glands  whereby  tears 
flow.  In  addition  to  muscles  and  glands,  elec< 
trie  organs  and  luminous  organs,  found  among 
fishes  and  other  lower  animals,  are  apparently 
also  reflexly  excitable. 


THE  NERVOUS  SYSTEM  17 

Reflexes  of  the  kind  just  mentioned  are  al- 
most invariably  congenital.  The  animal  is  born 
into  the  world  with  the  particular  reflex  mech- 
anism fully  formed  and  awaiting  merely  the 
appropriate  sensory  stimulation  that  the  new 
mechanism  may  come  into  full  operation.  The 
new-born  babe  sucks,  coughs,  and  sneezes 
without  lessons  or  advice.  Bees  artificially 
reared,  and  without  the  example  of  the  work- 
ing hive,  make  perfect  comb.  Many  female 
insects,  mostly  in  response  to  odors,  lay  their 
eggs  upon  materials  which  are  appropriate 
food  for  their  young.  Thus  a  great  variety 
of  animal  responses  have  the  qualifications  of 
simple  reflexes,  and  the  daily  life  of  many  of 
the  simpler  forms,  like  the  worms,  crabs,  in- 
sects, and  so  forth,  are  probably  made  up  al- 
most exclusively  of  this  kind  of  activity.  That 
these  responses  in  the  lower  animals  are  always 
associated  with  conscious  states  even  of  a  sim- 
ple kind  cannot  be  maintained  with  certainty, 
but  the  evidence,  on  the  whole,  indicates  that 
most  of  them  are  like  our  coughing,  or  the 
flow  of  tears  from  the  irritated  eye,  involun- 
tary operations,  but  with  the  stirrings  of  con- 
sciousness on  the  sensory  side. 

The  interrelations  of  these  reflexes  in  ani- 


18       BIOLOGY  AND  SOCIAL  PROBLEMS 

mals  midway  in  the  zoological  scale,  such  as 
the  insects,  for  instance,  are  not  without  in- 
terest. A  fly  in  the  neighborhood  of  food 
moves,  now  this  way,  now  that,  partakes  of 
a  little  moisture,  and,  if  disturbed  by  the  ap- 
proach of  a  person,  rises  in  the  air,  circles 
once  or  twice,  and  settles  near  the  food  to  be- 
gin again  its  irregular  foraging.  Evidently  in 
these  responses  smell,  touch,  and  sight  are 
in  continual  play  exciting  various  reflexes,  no 
one  class  of  which  predominates  over  another. 
There  is  a  condition  of  approximate  balance 
with  momentary  fluctuations,  now  this  way, 
now  that.  Catch  such  a  fly  in  the  hand  and, 
after  a  moment,  liberate  it ;  it  speeds  with  the 
utmost  rapidity  to  the  nearest  window.  To  the 
casual  observer  the  movements  of  the  fly  in 
foraging  were  of  the  same  mixed  nature  as 
those  which  we  exhibit  in  many  of  our  daily 
occupations,  and  the  rush  to  the  window  seems 
to  be  an  effort  to  escape.  But  the  same  rush 
is  made  to  a  closed  as  to  an  open  window,  and, 
if  the  room  in  which  the  trial  is  made  is  dark- 
ened by  having  the  blinds  drawn  and  is  illu- 
minated by  a  single  artificial  light,  the  rush  is 
made  not  at  the  window  or  even  at  the  open 
door,  if  it  leads  to  darkness,  but  at  the  source 


THE  NERVOUS  SYSTEM  19 

of  light,  even  though  the  fly  meets  its  death 
thereby.  Clearly  the  movements  of  the  fly  are 
not  so  like  those  of  a  human  being,  after  all. 
As  the  test  with  the  artificial  light  shows,  the 
animal  simply  seeks  light,  not  freedom.  To  be 
sure,  in  most  instances  to  fly  toward  the  light 
means  to  escape,  but  the  insect's  behavior  is 
rather  in  the  nature  of  a  reflex  than  of  a  cal- 
culated action,  and  in  that  sense  lacks  intelli- 
gence. The  fly,  like  many  other  animals  of  its 
own  rank,  is  ordinarily  in  a  state  of  what  may 
be  called  balanced  reflexes,  but  after  having 
been  especially  stimulated  by  being  caught 
and  roughly  handled,  this  balance  is  greatly 
disturbed  and  one  set  of  reflexes,  those  con- 
cerned with  flight  toward  the  light,  becomes 
supreme.  Under  such  circumstances  the  fly, 
without  reference  to  food,  drink,  or  other  fac- 
tor in  its  environment,  rushes  headlong  at  the 
most  considerable  light  within  its  range.  Of 
these  two  states,  the  one  of  balanced  and  the 
other  of  unbalanced  reflexes,  the  former  is 
more  nearly  representative  of  the  condition  in 
man,  though  at  first  sight  the  reverse  seems 
to  be  true. 

Turning  to  man,  it  is  evident  that,  not- 
withstanding his  many  powerful  and  assertive 


20       BIOLOGY  AND  SOCIAL  PROBLEMS 

reflexes,  he  is  not  so  much  within  the  grip 
of  these  agents  as  a  fly  is  under  the  dominance 
of  its  own  reflexes.  From  the  standpoint  of 
his  nervous  organization  he  is  a  much  more 
truly  balanced  organism  than  a  fly.  His  acts 
are  not  so  abundantly  purely  reflex,  but  the 
state  of  his  higher  nervous  activities  suggests 
not  only  a  condition  of  balanced  reflexes,  but 
vone  that  might  be  conceived  to  have  resulted 
from  the  disintegration  of  reflexes.  The  higher 
nervous  life  of  man,  his  intellectual  life,  seems 

1  built  upon  two  processes,  the  reception  of  im- 
pressions through  the  sensory  mechanism  of 
the  body,  and  the  production  of  voluntary  acts. 

\  These  two  operations  represent  in  a  way  the 
two  parts  of  a  reflex,  and  since  they  are  abun- 
dantly present  in  the  higher  nervous  activities 
of  the  human  being  in  an  essentially  independ- 
ent way,  it  is  possible  that  the  phylogenetic 
beginnings  of  this  form  of  intelligence  may 
have  been  associated  with  a  disintegration  of 
reflexes.  Certain  it  is  that  our  sense  organs 
are  almost  continuously  pouring  into  the  cen- 
tral organ  a  varied  stream  of  impulses  indica- 
tive of  the  changes  in  the  outside  and  yet  with- 
out calling  forth  any  obvious  responses  in  our 
musculature.  In  a  like  manner,  our  central  or- 


THE  NERVOUS  SYSTEM  *1 

gans  are  discharging  impulses  to  motion  with- 
out having  been  subjected  to  any  particular 
sensory  stimulation.  These  two  classes  of  ac- 
tivities are  continually  exhibited  in  our  higher 
nervous  life  and  afford  some  of  its  most  dif- 
ficult problems. 

So  far  as  our  intellectual  activities  are  con- 
cerned, our  sense  organs  may  be  said  to  be  re- 
ceiving incessantly  notices  of  external  changes 
and  to  be  transmitting  these  notices  to  the 
central  organs  rather  as  information  than  as 
incentives  to  action.  From  the  eyes,  the  ears, 
from  the  nose,  the  tongue,  from  the  organs 
of  touch,  from  the  cold  and  heat  spots, 
from  the  organs  of  pain  and  the  deep-lying 
muscle  receptors,  and  from  myriads  of  other 
and  unknown  sensory  mechanisms  a  steady 
flow  of  impulses  pours  into  the  central  organs. 
The  vast  volume  of  this  flood  is  of  no  spe- 
cial service  except  in  so  far  as  it  enables  us, 
partly  consciously  and  partly  unconsciously, 
to  adjust  ourselves  to  the  momentary  state  of 
the  environment.  But  certain  currents  in  the 
general  flow  influence  us  much  more  than  the 
rest  and  come  to  be  more  or  less  permanent 
eddies  in  our  mental  stream.  These  eddies  be- 
gin to  catch  in  early  childhood,  and  as  mem- 


22       BIOLOGY  AND  SOCIAL  PROBLEMS 

ories  continue  to  accumulate  throughout  life 
till  the  obliterations  of  old  age  and  death.  In 
many  respects  this  accumulation  is  most  di- 
verse, for  from  the  best  remembered  circum- 
stance to  the  fact  that  is  just  about  to  be  for- 
gotten there  is  every  gradation,  and  apparently 
no  circumstance  remains  long  in  the  same 
state  of  vividness,  but  all  is  drifting  toward 
oblivion,  some  portions  more  rapidly  than 
others,  while  the  new  is  ever  replacing  the 
old. 

In  practical  life  we  come  to  regard  our  re- 
membrances as  having  a  certain  degree  of  com- 
pleteness, but  in  reality  they  are  the  merest 
shred  of  our  past.  Think  of  a  vivid  experience 
in  the  last  ten  years  or  so  and  recount  to  your- 
self the  occurrences  of  the  day  on  which  it 
happened.  Very  little  but  the  most  shadowy 
outline  is  left.  Even  yesterday,  so  near  at 
hand,  is  mostly  gone,  and  as  a  test  for  the  pres- 
ent who  among  us  here  can  give  again  from 
memory  the  first  sentence  of  this  lecture? 
We  all  heard  it  and  I  read  it,  but  even  I  can- 
not repeat  it.  Yet  if  memory  were  in  this  re- 
spect only  as  perfect  as  a  dictagraph,  this  sen- 
tence could  be  recovered  from  every  one  in 
the  room.  I  am  fully  aware  that  in  certain 


THE  NERVOUS  SYSTEM  23 

unusual  mental  states,  such  as  hypnosis,  the 
individual  can  deliver  information  about  mat/- 
ters  which  in  his  normally  wakeful  condition 
he  seems  to  be  incompetent  to  produce,  and 
that  in  this  way  evidence  of  memory  activity 
in  the  subconscious  regions  of  the  mind  is  ad- 
duced. But  that  this  additional  accumulation 
would  bring  the  shadowy  past  into  anything 
like  the  completeness  of  the  present  is  not  for 
a  moment  to  be  imagined.  Marvelous  as  all 
these  processes  are,  in  that  they  are  sugges- 
tive of  hidden  and  unseen  powers,  we  must 
still  admit,  I  believe,  that  memory  at  best  is 
a  most  fragmentary  affair.  This  opinion  is 
well  expressed  by  Walt  Whitman  when,  in 
speaking  of  the  insufficiency  of  biography,  he 
declares  — 

Why,  even  I  myself,  I  often  think,  know  little  or 

nothing  of  my  real  life ; 
Only  a  few  hints  —  a  few  diffused,  faint  clues  and 

indirections. 

But  fragmentary  as  memory  is,  it  is  that 
which  binds  our  personality  together ;  without 
it  social  responsibility  would  cease  to  exist. 
We  admit  its  frailness  by  translating  our  ideas 
into  the  permanency  of  the  written  record. 
This  supplement  to  memory  penetrates  our 


24       BIOLOGY  AND  SOCIAL  PROBLEMS 

whole  life,  from  the  memorandum  on  a  scrap 
of  paper  to  the  inscription  on  the  living  rock, 
and  thus  aids  enormously  one  of  our  mental 
processes  at  its  weakest  point. 

How  is  memory  related  to  the  nervous  sys- 
tem ?  By  appropriate  methods  of  experimen- 
tation we  can  determine  with  great  accuracy 
the  tracts  of  the  nervous  system  over  which  a 
given  reflex  runs.  Is  such  a  localization  pos- 
sible for  memory,  or  is  this  function  rather  the 
general  property  of  the  nervous  system  as  a 
whole?  Strange  as  it  may  seem,  memory  is 
almost  if  not  quite  the  exclusive  function  of 
one  part  of  our  nervous  organs,  namely,  the 
cerebral  cortex.  This  gray  layer  covers  the  ex- 
terior of  the  cerebral  hemispheres  and  thus 
lies  on  the  surface  of  the  brain  separated  from 
the  outer  world  by  only  the  skull  and  the 
superimposed  scalp.  In  man  it  varies  in  thick- 
ness from  one  and  a  half  to  five  millimeters 
and  covers  a  convoluted  field,  which,  were  it 
flattened  out,  would  measure  on  the  average 
2352  square  centimeters,  equal  to  an  area  a 
little  over  a  foot  and  a  half  square.  This  re- 
markable layer  is  the  organ  in  which  all  our 
sensations  arise  and  where  the  processes  of 
memory  go  on.  It  is,  therefore,  the  location 


THE  NERVOUS  SYSTEM  *5 

of  one  of  the  most  important  aspects  of  per- 
sonality. 

Experimental  demonstrations  of  this  truth 
have  been  abundantly  carried  out.  By  a  care- 
ful surgical  operation  the  cerebral  cortex  of  a 
bird  or  even  of  a  mammal,  such  as  a  dog,  can 
be  removed  and  the  animal  can  be  kept  alive 
for  as  much  as  a  year  or  more  after  the  oper- 
ation. Such  animals  yield  most  important 
evidence  as  to  the  function  of  the  cerebral 
cortex.  After  recovery  from  the  operation, 
they  exhibit  no  permanent  motor  disturbances, 
such  as  paralyses  and  so  forth,  and  they  re- 
spond to  practically  all  forms  of  stimulation, 
but  their  responses  are  not  what  would  be 
called  intelligent.  A  pigeon  from  which  the 
cortex  has  been  removed,  when  placed  on  a 
hot  plate  will  raise  first  one  foot,  then  the 
other,  and  finally  squat  rather  than  fly  away. 
A  dog  without  a  cortex  will  respond  to  a 
painful  stimulation  of  the  skin  by  a  growl  or 
a  bark  and  will  turn  its  head  toward  the  spot 
stimulated,  but  will  not  attempt  to  bite.  Ca- 
ressing calls  forth  no  sign  of  pleasure,  threat- 
ening no  sign  of  fear.  In  sleep  there  is  no 
evidence  of  dreaming.  Such  animals  thus  re- 
spond to  the  immediate  stimulus,  but  as 


26        BIOLOGY  AND  SOCIAL  PROBLEMS 

though  they  were  without  experience  and  in  a 
way  essentially  stupid.  Memory  seems  to  have 
vanished  from  them  and  with  it  the  basis  for 
intelligent  action.  The  animal  responds  to 
stimulation  like  a  nervous  machine  and  with- 
out reference  to  past  or  future. 

What  it  is  that  the  cortex  contains  and 
that  molds  our  responses  into  intelligent  acts 
is  our  store  of  experience.  During  normal  life, 
as  we  have  already  seen,  a  flood  of  impulses 
due  to  the  stimulation  of  sense  organs  by  ex- 
ternal changes  pours  into  the  central  nervous 
organs ;  many  of  these  reach  the  cortex  and 
some  leave  on  this  organ  a  more  or  less  per- 
manent impression.  These  elemental  impres- 
sions are  the  materials  out  of  which  our  men- 
tal life  is  built.  All  our  thinking  is  made  up 
of  a  redistribution  and  readjustment  of  these 
elements.  From  the  highest  flights  of  poetic 
imagination,  from  the  aspirations  of  the  most 
devout  to  the  extreme  speculations  of  the 
philosopher,  mathematician,  and  devotee  of 
science,  all  are  but  readjustments  and  deriva- 
tions of  this  mass  of  incoming  material.  With- 
out this  spring  of  supply  the  human  brain 
would  be  a  barren  and  arid  waste  incapable 
of  bringing  forth  signs  of  intelligence.  The 


THE  NERVOUS  SYSTEM  27 

brain  of  the  developing  child  is  a  veritable  ta- 
bula rasa  on  which  environment  through  the 
sense  organs  writes  the  story  of  life.  Innate 
ideas  there  are  none.  The  uninvaded  mind  is 
like  a  machine  in  readiness  for  operation,  but 
awaiting  the  arrival  of  that  first  flow  of  power 
to  initiate  its  processes.  Like  the  lung,  it 
stands  in  perfect  physical  readiness  for  action ; 
at  birth  the  stimulus  for  the  first  inspiration 
occurs  and  the  respiratory  mechanism  that  is 
to  run  till  the  end  of  life  is  started. 

In  stating  briefly  the  modern  conception 
concerning  the  source  of  the  contents  of  the 
mind,  I  have  put  the  matter  almost  in  the 
words  of  Locke,  but  the  present  aspect  of  this 
subject  is  not  based  upon  philosophical  spec- 
ulation ;  it  is  grounded  upon  observed  fact.  We 
know  that  when  we  sleep  we  revert  to  a  con- 
dition of  relatively  simple  reflexes  and  that 
intelligence  vanishes  in  the  assumption  of  the 
unconscious  state.  To  induce  this  condition 
under  normal  circumstances,  we  check  as  far 
as  possible  aU  sensory  inflow  by  lying  down 
in  a  darkened,  quiet  situation.  The  impulses 
from  the  organs  of  touch,  equilibrium,  and 
especially  of  hearing  and  sight,  having  been 
reduced  to  a  minimum,  the  activity  of  the 


28       BIOLOGY  AND  SOCIAL  PROBLEMS 

cortex  quickly  subsides,  and  with  this  sub- 
sidence consciousness  gives  place  to  uncon- 
sciousness. Thus,  even  a  mind  stored  with  rec- 
ollections lapses  into  unconsciousness  when, 
under  appropriate  conditions,  the  flow  of  new 
material  from  without  is  largely  reduced.  Not 
only  does  the  inflow  of  sensory  impulses  thus 
condition  the  activity  of  the  normal  mind,  but 
it  has  also  been  found  to  be  of  like  importance 
in  certain  abnormal  cases.  Striimpeirs  boy 
was  a  defective  who  was  insensitive  to  touch, 
had  no  muscular  sense,  no  taste,  or  smell,  or 
sense  of  pain,  and  was  deaf  in  the  right  ear 
and  blind  in  the  left  eye.  His  sensory  impulses 
were  received  therefore,  chiefly  if  not  exclu- 
sively, through  the  left  ear  and  the  right  eye. 
If  the  left  ear  was  stopped  and  the  right  eye 
bandaged,  so  that  the  sensory  inflow  practi- 
cally ceased,  he  passed  in  a  few  minutes  into 
what  seemed  to  be  a  state  of  sleep,  thus  dem- 
onstrating the  significance  of  the  current  from 
the  sense  organs  for  his  mental  life.  The  ab» 
normal,  as  well  as  the  normal,  thus  gives  evi- 
dence of  the  general  conclusion  that,  though 
the  mode  of  operation  of  the  mind  may  be 
determined  by  the  inborn  structure  of  the 
brain,  the  content  of  the  mind  is  supplied 


THE  NERVOUS  SYSTEM  29 

ultimately  through  sensory  impulses  from  the 
exterior. 

Fragmentary  and  incomplete  as  memory  is, 
its  performances  continually  excite  our  won- 
der and  curiosity,  and  even  from  the  scien- 
tific standpoint  we  are  prone  to  speculate  on 
the  methods  by  which  it  is  brought  about. 
Our  common  habit  of  recording  and  storing 
as  evidence  of  our  experience  written  or 
printed  signs  has  given  us  a  figurative  concep- 
tion of  the  process  of  memory  which  is  in 
many  respects  misleading.  We  often  think  of 
the  organ  of  memory,  the  cortex,  as  a  place  in 
which  is  set  aside,  in  some  such  manner  as 
that  just  indicated,  signs  of  our  experience  to 
be  drawn  upon  as  needed.  But  the  cortex  is 
a  living  portion  of  our  body,  and,  like  other 
living  parts,  its  life  is  expressed  better  in  its 
activity  than  in  its  structure,  for  its  structure 
is  forever  changing.  Memory,  therefore,  is 
rather  a  duplication  of  a  process  than  the  re- 
appearance of  a  symbol.  It  is  rather  like  a 
current  eddy  in  the  flow  of  our  mental  life 
than  like  a  material  sign.  But  it  is  an  eddy 
which  only  partially  represents  the  original 
and  carries  with  it  something  that  separates 
it  from  real  present  experience  and  marks  it 


30       BIOLOGY  AND  SOCIAL  PROBLEMS 

as  a  shadow  of  the  past.  What  memory  really 
is,  however,  is  rather  a  matter  for  investiga- 
tion than  speculation.  Of  one  thing  we  can 
be  fairly  certain,  memory  is  not  a  general 
property  of  the  nervous  system,  but  is  an  op- 
eration carried  on  in  the  cerebral  cortex. 

This  portion  of  the  brain  is  also  the  part 
concerned  with  that  second  set  of  operations 
which  seem  to  result  from  the  disintegration 
of  simple  reflexes,  namely,  the  voluntary  acts. 
That  the  impulses  to  voluntary  movements  in 
man  take  their  course  from  the  cerebral  cortex, 
over  definite  neurone  tracts  through  the  cord 
and  nerves  to  the  muscles  concerned,  is  a  fact 
well  attested  by  anatomy,  pathology,  and  the 
study  of  cortical  localization.  But  it  is  not  my 
purpose  to  undertake  to  trace  out  the  nervous 
mechanism  by  which  we  control  that  enor- 
mous complication  of  musculature  that  moves 
when  we  wish  to  move,  and  that  fails  to  act 
when  by  reason  of  accident  or  disease  nerve 
tracts  are  interfered  with  or  destroyed.  Suffice 
it  to  say  that  the  impulses  for  the  multitude 
of  our  voluntary  acts  emanate  from  the  cortex. 
Whether  they  originate  there  de  novo,  or  are 
some  delayed  overtime  sensory  impulses  mak- 
ing their  way  deliberately  through  the  central 


THE  NERVOUS  SYSTEM  31 

organs  to  a  final  effective  outcome,  cannot  be 
stated,  and  is  perhaps,  after  all,  a  question  of 
no  significance.  For  the  nervous  system,  even 
at  its  lowest  physiological  ebb,  is  never  quies- 
cent. It  exhibits  continuous  activity.  Even 
in  sleep  our  muscles  show  a  slight  contraction 
due  to  a  faint  but  incessant  stimulation  from 
the  nervous  centers.  The  passage  of  a  reflex 
impulse  through  the  nervous  system,  then,  is 
not  so  much  like  a  brief  period  of  activity  in 
an  otherwise  motionless  machine  as  it  is  like 
a  momentary  increase  of  motion  in  a  slow  con- 
tinuous operation.  From  such  a  continuum 
the  voluntary  impulses  emerge.  To  seek  their 
origin  is  perhaps  to  look  for  that  which  does 
not  exist,  at  least  in  the  definite  and  crystal- 
lized form  in  which  we  often  think  of  it. 

Just  as  memory  affords  a  most  taxing  and 
perplexing  problem  for  science,  so  the  volun- 
tary act  is  a  process  about  which  there  is  very 
little  real  understanding.  The  difficulty  lies  in 
its  freedom.  Such  acts  give  us  every  evidence 
both  outward  and  inward  of  self-control.  They 
seem  to  be  self -determining  and  in  this  respect 
to  violate  those  principles  of  sequence  that  we 
find  to  underlie  so  much  of  nature. 

Attempts  have  been  made  to  show  that  the 


32       BIOLOGY  AND  SOCIAL  PROBLEMS 

freedom  of  the  voluntary  act  is  not  without 
its  counterpart  in  the  more  rigid  aspects  of 
science.  The  answer  to  the  question  what  two 
digits  will  add  together  to  make  ten  is  not 
single,  but  may  be  with  equal  truth  any  one 
of  several ;  four  and  six  is  as  correct  an  an- 
swer as  eight  and  two.  But  this  kind  of  free- 
dom is  after  all  a  formal  freedom  in  a  mental 
operation  rather  than  a  freedom  in  a  material 
sequence  in  nature. 

From  the  standpoint  of  science  the  solution 
of  the  problem  of  the  voluntary  act,  like  that 
of  memory,  is  to  be  sought  in  investigation 
rather  than  speculation.  But  the  scientific 
study  of  this  question  must  be  undertaken 
without  prejudice.  Physics  and  chemistry  are 
branches  of  science  to  which  the  biologist  has 
come  to  attribute  a  certain  fundamental  im- 
portance in  that  organisms  are  believed  to  be 
enormously  complex  physico-chemical  combi- 
nations. Day  by  day  facts  of  organic  nature 
are  yielding  to  this  conception,  and  such  prog- 
ress is  being  made  as  to  give  rise  in  the 
minds  of  many  investigators  to  the  opinion 
that  in  the  end  all  will  thus  be  subdued.  But 
voluntary  acts,  if  not  incorrectly  described, 
seem  to  be  fundamentally  contrary  to  the  gen- 


THE  NERVOUS  SYSTEM  S3 

eral  principles  of  physics  and  chemistry,  and 
are,  therefore,  grounds  for  opposition  to  the 
opinion  just  alluded  to.  However,  in  consid- 
ering this  opposition  it  must  not  be  forgotten 
that  these  sciences  are  still  in  process  of  ac- 
tive growth,  and  that  what  we  regard  as  their 
general  principles  to-day  are  principles  devel- 
oped chiefly  from  a  study  of  inorganic  na- 
ture. In  only  a  most  tentative  way  have  these 
sciences  begun  to  touch  matter  and  energy  as 
exhibited  in  organisms.  How  their  principles 
will  be  modified  when  they  really  begin  a  suc- 
cessful attack  on  living  beings  remains  to  be 
seen,  but  that  these  principles  will  be  modified 
there  can  be  not  the  least  doubt.  Then  will  be 
the  time  to  raise  the  question  of  the  nature 
of  the  voluntary  act  and  other  such  problems  if, 
indeed,  these  problems  really  remain  serious 
in  the  light  of  the  new  knowledge,  for  often 
what  seems  to  be  a  perplexing  question  to-day 
becomes  insignificant  to-morrow.  Who  con- 
cerns himself  now  with  the  number  of  angels 
that  can  stand  on  the  point  of  a  needle  ? 

But  I  cannot  leave  this  matter  of  memory 
and  the  voluntary  operations  without  consid- 
ering somewhat  further  the  part  of  the  human 
nervous  system  in  which  these  functions  occur. 


34       BIOLOGY  AND  SOCIAL  PROBLEMS 

The  human  cerebral  cortex,  as  already  men- 
tioned, is  a  superficial  layer  of  the  brain  with 
a  thickness  varying  from  one  and  a  half  to 
five  millimeters  and  covering  an  average  of 
2352  square  centimeters.  This  cortex  is  esti- 
mated to  weigh  about  658  grammes.  It  is 
composed  chiefly  of  blood  vessels,  supporting 
tissues,  and  nerve  cells.  The  blood  vessels  and 
supporting  tissues  are  merely  mechanical  ac- 
companiments of  an  apparatus  the  real  func- 
tions of  which  are  carried  on  by  the  nerve 
cells.  These  cells  have  been  carefully  studied, 
their  arrangement  and  distribution  made  out, 
and  it  is  estimated  that  in  a  single  cortex 
their  number  is  not  far  from  9,200,000,000. 
Notwithstanding  this  prodigious  number, 
these  cells  and  their  processes  represent  only 
two  per  cent  of  the  total  weight  of  the  cor- 
tex ;  in  other  words,  the  cortical  nerve  cells 
and  their  processes  in  the  average  man  weigh 
about  thirteen  grammes.  This  amount  repre- 
sents a  little  less  than  a  cubic  inch  of  mate- 
rial, or,  to  be  more  accurate,  it  will  just  fill  a 
cube  whose  edge  is  2.35  centimeters.  In  a  man 
who  weighs  approximately  one  hundred  and 
fifty  pounds,  this  amount  of  substance  would 
represent  about  one  five-thousandth  of  his 


THE  NERVOUS  SYSTEM  35 

total  weight,  yet  this  very  small  proportion  of 
his  body  serves  him  as  the  material  basis  for  a 
whole  life  of  intelligent  activity  and  is  the  part 
of  the  nervous  system  chiefly  concerned  in 
yielding  that  almost  impalpable  product,  hu- 
man personality.  Had  Descartes  been  truly 
scientific,  and  had  he  known  in  his  time  the 
anatomy  and  physiology  of  the  nervous  sys- 
tem as  it  is  known  to-day,  he  would  have  de- 
clared that  the  cerebral  cortex  and  not  the 
pineal  body  was  the  seat  of  the  soul. 

From  the  foregoing  sketch  some  idea  can 
be  gathered  of  the  significance  of  the  nervous 
system  for  man  as  a  social  organism  and  of 
the  part  it  plays  in  his  daily  life.  From  a  back- 
ground of  simple  reflexes  which  attend  to  a 
long  range  of  his  bodily  needs,  and  which 
are  unassociated  or  only  slightly  associated 
with  consciousness,  rise  the  superstructures 
concerned  with  his  higher  nervous  functions 
such  as  memory  and  voluntary  action.  These 
general  nervous  functions  have  done  more  to 
make  an  individual  of  him  than  any  other  el- 
ements in  his  nature.  His  circulatory  mechan- 
ism with  its  centralized  heart  has  added  much 
to  this  unity,  but  even  such  organs  are  secon- 
dary to  the  nervous  system.  When  we  reflect 


36       BIOLOGY  AND  SOCIAL  PROBLEMS 

that  many  of  the  lower  animals,  like  the  sea 
anemones,  for  instance,  have  only  the  merest 
rudiments  of  a  nervous  system,  and  that  this 
system  is  there  concerned  simply  in  calling 
muscles  into  action  and  exhibits  practically 
no  central  functions,  we  begin  to  appreciate 
how  strikingly  different  the  conditions  are  in 
higher  and  lower  forms.  Each  tentacle  of  a 
sea  anemone  contains  its  own  neuro-muscular 
mechanism  and  will  continue  to  respond  to 
food  particles  after  it  has  been  severed  from 
the  body.  Its  action  is  as  independent  of  the 
rest  of  the  animal  as  the  vertebrate  heart  is  of 
the  body  in  which  it  grew.  But  the  sea  anem- 
one, instead  of  possessing  only  a  few  such 
organs  as  the  vertebrate  does,  is  constructed 
almost  entirely  upon  this  plan.  Its  nervous 
functions  are  most  diffuse  and  subordinate ; 
its  chief  activities  are  feeding  and  reproduc- 
tion. If  man  can  be  described  as  an  organism 
whose  tour-de-force  is  intellectual,  the  sea 
anemone  is  one  whose  culminating  activities  are 
assimilation  and  growth.  This  condition  of 
affairs  is  characteristic  of  most  of  the  lower  an- 
imals and  represents  unquestionably  a  primitive 
stage  before  which  the  nervous  system  could 
scarcely  be  said  to  have  existed.  In  the  higher 


THE  NERVOUS  SYSTEM  37 

forms,  however,  this  system  has  far  outstripped 
the  others  in  its  growth,  till  in  the  mammals 
and  especially  in  man  it  has  reached  a  position 
of  supreme  dignity.  Thus  the  nervous  system, 
though  it  originated  later  than  some  other  sets 
of  organs,  has  in  the  higher  forms  attained  to 
paramount  importance. 

With  the  evolution  of  the  nervous  system 
and  the  differentiation  of  the  cerebral  cortex 
came  the  possibilities  of  that  form  of  compli- 
cated intellectual  life  that  we  know  in  our- 
selves. Though  less  than  a  cubic  inch  of  our 
substance  is  really  devoted  to  this  form  of  ac- 
tivity, it  is  as  precious  a  cubic  inch  as  any  we 
possess.  By  means  of  it  we  cherish  the  tradi- 
tions of  the  past ;  its  activities  include  all  our 
conscious  states,  our  simple  sensations,  desires, 
hopes,  and  aspirations,  our  sense  of  shame  and 
regret  at  deeds  of  unworthiness,  our  joy  in 
generous  acts,  our  knowledge  of  all  these 
things;  from  it  emanate  the  impulses  to 
those  steps  which  mark  us  as  dishonest  or  hon- 
est, extravagant  or  thrifty,  secretive  and  de- 
ceptive or  frank,  open,  and  free,  cold  or  affec- 
tionate, in  short  all  those  signs  which  stand 
for  personality.  Socially  no  part  of  our  body 
is  more  precious  than  this  cubic  inch  of  cortex. 


88       BIOLOGY  AND  SOCIAL  PROBLEMS 

From  the  cradle  to  the  grave  we  work  to  train 
it.  Our  early  childish  plays  and  lessons  are  in- 
tended to  awaken  it  into  activity.  The  school, 
the  college,  the  university  work  upon  it ;  our 
whole  educational  system  is  devised  to  bring 
into  full  efficiency  this  cubic  inch  of  our  body. 
It  must  be  enriched  with  experience ;  it  must 
be  trained  to  make  wise  decisions,  to  call  forth 
acts  of  friendly  service.  If  you  have  doubts 
of  the  enormous  social  significance  of  this  cu- 
bic inch  of  nervous  tissue,  look  upon  the  in- 
dividual in  which  it  permanently  breaks  down, 
a  useless  member  of  society,  a  charge  upon 
the  state,  if  not  upon  the  race. 


II 

HOKMONES 

IN  olden  times  the  theory  and  practice  of 
medicine  was  more  or  less  permeated  by  the 
doctrine  of  the  humors.  Those  of  you  who 
are  conversant  with  medical  history  will  recall 
that,  according  to  this  doctrine,  there  were 
supposed  to  be  four  cardinal  humors :  blood, 
yellow  bile  or  choler,  phlegm,  and  black  bile. 
Many  distempers  of  mind  and  body  were  at- 
tributed to  disturbances  in  these  fluids,  and 
their  conditions  and  proportions  were  sup- 
posed to  determine  the  physical  and  mental 
qualities  as  well  as  the  disposition  of  the  indi- 
vidual. Various  kinds  of  insanity,  known  un- 
der the  general  name  of  melancholy,  were 
supposed  to  be  associated,  as  this  term  implies, 
with  the  black  bile.  And  we  still  describe  tem- 
peraments as  sanguine,  choleric,  or  phleg- 
matic. But  with  the  growth  of  our  knowledge 
of  the  nervous  system  and  with  the  recognition 
of  its  significance  as  the  chief  means  of  con- 
trol for  the  body  as  well  as  the  seat  of  person- 


40       BIOLOGY  AND  SOCIAL  PROBLEMS 

ality,  the  doctrine  of  the  humors  was  relegated 
to  the  rubbish  heap  of  worn-out  ideas  and  dis- 
appeared from  view.  Within  late  years,  how- 
ever, this  doctrine,  in  principle  at  least,  has 
been  revived,  and  recent  investigations  prom- 
ise to  give  it  renewed  life,  though  not  of  such 
general  scope  as  it  once  enjoyed.  The  fluids 
circulating  in  the  bodies  of  animals,  including 
man,  are  undoubtedly  highly  important  and 
significant  means  of  controlling  the  responses 
of  these  forms  and  of  determining  their  states, 
mental  and  otherwise.  Among  the  recent  dis- 
coveries which  have  been  important  in  open- 
ing up  this  point  of  view  are  those  concerning 
the  action  of  the  pancreas,  a  gland  which  was 
supposed  to  be  brought  into  activity  through 
the  ordinary  channels  of  nervous  reflex. 

The  pancreas  is  a  long,  narrow  gland  ex- 
tending from  the  neighborhood  of  the  spleen 
on  the  left  side  of  the  abdomen  to  the  right 
side  of  that  cavity  where  its  duct  opens  into 
that  portion  of  the  small  intestine  known  as 
the  duodenum.  This  opening  is  three  or  four 
inches  from  the  outlet  of  the  stomach,  there- 
fore near  the  beginning  of  the  duodenum,  and 
very  close  to  the  opening  of  the  bile  duct  from 
the  liver.  The  pancreas  is  popularly  known  as 


HORMONES  41 

the  sweetbread,  or,  better,  the  stomach  sweet- 
bread, to  distinguish  it  from  the  thyroid  gland 
which  is  called  by  butchers,  from  its  location, 
throat  sweetbread. 

The  pancreas  in  man  produces  a  copious 
secretion,  as  much  as  from  five  hundred  to 
eight  hundred  cubic  centimeters  per  day. 
This  secretion  is  poured  into  the  duodenum 
through  the  pancreatic  duct  and  is  one  of  the 
most  important  digestive  juices.  It  aids  in  the 
solution  of  almost  all  the  constituents  of  our 
food.  The  pancreatic  juice  is  apparently  pro- 
duced in  small  amounts  continuously,  but  the 
major  production  and  discharge  is  associated 
with  the  taking  of  food.  The  increase  of  pro- 
duction begins  soon  after  food  has  entered 
the  stomach  and  develops  to  a  maximum  in 
from  two  to  four  hours;  it  then  gradually 
falls  off  with  the  completion  of  digestion. 

Almost  two  decades  ago  it  was  shown  that 
when  acid  solutions  were  applied  to  the  mu- 
cous surface  of  the  duodenum,  the  flow  of  pan- 
creatic juice  was  excited,  and  as  the  natural 
contents  of  the  stomach  are  acid,  it  was  be- 
lieved that,  after  they  had  passed  into  the 
duodenum,  their  acidity  was  the  normal  stim- 
ulus for  the  reflex  mechanism  controlling  the 


42       BIOLOGY  AND  SOCIAL  PROBLEMS 

pancreas.  As  the  food  arrived  in  the  duodenum 
from  the  stomach,  the  contained  acid  was  sup- 
posed to  stimulate  the  nerve  terminals  in  the 
mucous  membrane  of  that  portion  of  the  in- 
testine and  thus  to  set  up  nerve  impulses  which 
were  reflected  back  from  the  central  organs 
to  the  gland  as  excitants  of  its  activity.  This 
opinion  was  consonant  with  the  fact  that  arti- 
ficial stimulation  of  the  vagus  nerve  was  fol- 
lowed by  pancreatic  secretion.  But  the  secre- 
tion of  juice  by  the  pancreas  was  subsequently 
shown  also  to  occur  even  after  the  nerves 
which  supply  that  organ,  namely,  the  vagus 
and  the  splanchnic,  were  cut. 

The  difficulty  thus  introduced  was  removed 
by  the  work  of  Bayliss  and  Starling  about  a 
decade  ago.  They  demonstrated  that  if  some 
of  the  mucous  membrane  of  the  duodenum 
was  scraped  off  and  mixed  with  a  weak  solu- 
tion of  acid,  an  extract  could  be  obtained 
which  when  injected  into  the  blood  would  call 
forth  an  active  secretion  of  pancreatic  juice 
even  in  an  animal  in  which  the  nerves  to  the 
pancreas  had  been  severed.  Hence  they  con- 
cluded that  the  secretory  activity  of  the  pan- 
creas was  not  necessarily  dependent  upon 
nerves,  but  could  be  induced  by  a  substance 


HORMONES  43 

which  resulted  from  the  action  of  the  acid 
food  on  the  mucous  walls  of  the  intestine  and 
which  was  taken  up  by  the  blood  and  in  this 
way  carried  to  the  gland.  Thus,  what  seemed 
to  be  a  reflex  action  proved  in  reality  to  be 
the  effect  upon  one  organ  of  a  substance 
formed  in  another.  The  particular  substance 
in  the  case  of  the  pancreas  is  known  as  secre- 
tin.  This  substance  is  not  of  the  nature  of  an 
enzyme,  for  it  is  not  destroyed  by  boiling 
or  by  treatment  with  alcohol.  It  is,  however, 
a  representative  of  what  is  probably  a  large 
class  of  substances  now  recognized  under  the 
general  name  of  hormones,  whose  function  it 
is  to  excite  activity  in  organs  usually  situated 
at  a  distance  from  the  region  in  which  the 
given  hormone  is  produced ;  in  other  words, 
to  enable  one  part  of  the  organism  to  control 
another  and  distant  part.  As  is  shown  by  the 
pancreas,  hormone  action  strikingly  simulates 
in  its  results  nervous  activity,  and  yet  on  an 
entirely  different  principle,  a  principle  which 
in  fact  revives  the  discarded  doctrine  of  the 
humors. 

The  extent  to  which  hormones  control  the 
body  is  only  just  beginning  to  be  appreciated. 
For  a  long  time  anatomists  have  recognized 


44       BIOLOGY  AND  SOCIAL  PROBLEMS 

in  the  higher  animals,  including  man,  a  num- 
ber of  so-called  ductless  glands,  such  as  the 
thyroid  gland,  the  pineal  gland,  the  hypophy- 
sis, the  adrenal  bodies,  and  so  forth.  These 
have  often  been  passed  over  as  unimportant 
functionless  organs  whose  presence  was  to  be 
explained  as  an  inheritance  from  some  remote 
ancestor.  But  such  a  conception  is  far  from 
correct.  If  the  thyroids  are  removed  from  a 
dog,  death  follows  in  from  one  to  four  weeks. 
If  the  adrenal  bodies  are  excised,  the  animal 
dies  in  from  two  to  three  days.  Such  results 
show  beyond  doubt  that  at  least  some  of  these 
organs  are  of  vital  importance,  and  more  re- 
cent studies  have  demonstrated  that  most  of 
them  produce  substances  which  have  all  the 
properties  of  hormones.  A  number  of  these 
organs,  like  the  thyroids,  the  adrenals,  and 
the  sexual  glands,  have  been  studied  from  the 
standpoint  of  their  internal  secretions  and 
have  more  than  a  passing  biological  interest. 
The  thyroid  gland  in  man  consists  of  two 
moderately  large  lobes  closely  applied  to  either 
side  of  the  windpipe  just  below  the  larynx  or 
Adam's  apple.  As  previously  stated,  the  gland 
is  popularly  known  as  the  throat  sweetbread 
in  contrast  with  the  stomach  sweetbread  or 


HORMONES  45 

pancreas.  The  two  lobes  of  the  thyroid  are 
united  across  the  front  of  the  windpipe  by  a 
narrow  band  of  their  own  substance,  the  so- 
called  isthmus.  The  thyroid  gland  is  inti- 
mately associated  with  a  group  of  glands,  the 
parathyroids,  whose  presence  was  not  always 
recognized  by  the  earlier  investigators.  Some 
of  the  confusion  which  entered  into  the  ear- 
lier physiological  work  on  the  thyroid  was 
probably  due  to  the  accidental  removal  of  the 
parathyroids  with  the  thyroid,  a  condition 
which  leads  to  very  different  results  from 
those  observed  in  the  simple  removal  of  the  thy- 
roid itself.  The  circumstances  which  brought 
about  an  investigation  of  the  thyroid  may  now 
be  briefly  stated. 

In  any  large  community  individuals  appear 
from  time  to  time  who  from  childhood  on  fail 
to  grow  and  develop.  They  therefore  are  of 
dwarfish  stature,  their  hands  are  large  and 
misshapen,  their  features  dull  and  expression- 
less. All  these  signs,  together  with  the  actions 
and  habits  of  such  individuals,  give  the  im- 
pression to  the  casual  observer  of  low  mental 
capacity,  if  not  idiocy,  and  such  in  truth  is 
their  real  state.  As  members  of  society  they 
are  usually  more  or  less  helpless  and  are  either 


46       BIOLOGY  AND  SOCIAL  PROBLEMS 

private  or  public  charges.  They  have  long 
been  known  under  the  name  of  cretins. 

An  examination  of  the  physical  condition 
of  these  persons  has  disclosed  the  significant 
fact  that  they  all  possess  deficient  thyroid 
glands,  and  this  discovery  has  led  to  the  as- 
sumption that  the  thyroid  produces  a  hormone 
which  is  essential  to  the  growth  and  devel- 
opment of  the  normal  person.  This  belief  is 
abundantly  supported  by  the  success  with 
which  cretinism  and  tendencies  toward  cretin- 
ism can  be  in  large  part  counteracted  by  thy- 
roid treatment.  Many  of  our  so-called  defec- 
tive children  are  known  to  be  cases  in  which 
thyroid  activity  is  reduced,  and  they  approxi- 
mate in  many  ways  a  mild  form  of  cretinism. 
In  these  cases,  as  well  as  in  true  cretinism,  the 
feeding  of  the  patient  with  thyroid  material, 
with  the  throat  sweetbreads  of  sheep,  has  been 
followed  almost  invariably  by  most  beneficial 
results  both  physical  and  intellectual.  In  this 
way  children  on  a  downward  path  of  develop- 
ment have  been  rescued  from  a  trying  form 
of  dissolution. 

Defective  thyroids,  however,  are  not  limited 
to  childhood ;  they  may  appear  in  adult  life. 
At  this  stage  they  cannot,  of  course,  produce 


HORMONES  47 

cretinism,  but  in  other  respects  they  call  forth 
the  same  set  of  changes ;  intelligence  declines 
even  to  dementia ;  bodily  activity  subsides  till 
only  animal  sluggishness  is  left ;  a  condition  ••• 
known  as  myxedema  supervenes,  after  which 
in  the  course  of  some  years  the  cases  termin- 
ate fatally.  These  mature  cases  are  also  im- 
mensely alleviated  by  the  thyroid  treatment. 
In  cases  of  myxedema  it  was  found  that  in- 
jection of  thyroid  extract  under  the  skin,  or 
better  still,  simple  feeding  of  thyroid  mate- 
rial, gave  favorable  results.  Only  from  sixty  to 
one  hundred  and  thirty  milligrams  of  sub- 
stance administered  every  three  or  four  days 
was  found  sufficient  to  keep  a  patient  in 
health. 

I  cannot  better  picture  to  you  the  signifi- 
cance of  this  treatment  both  for  the  child  and 
the  adult  than  by  quoting  from  Moore  the 
words  of  a  well-known  medical  authority,  Dr. 
Willia'm  Osier,  who,  in  speaking  of  this  side 
of  medicine,  has  said :  "  Our  art  has  made  no 
more  brilliant  advance  than  in  the  cure  of 
these  disorders  due  to  the  disturbed  function 
of  the  thyroid  gland.  That  we  can  to-day  res- 
cue children  otherwise  doomed  to  helpless 
idiocy,  that  we  can  restore  to  life  the  hopeless 


48       BIOLOGY  AND  SOCIAL  PROBLEMS 

victims  of  myxedema,  is  a  triumph  of  experi- 
mental medicine."  "  The  results  as  a  rule  are 
most  astounding — unparalleled  by  anything  in 
the  whole  range  of  curative  measures.  Within 
six  weeks  a  poor,  feeble-minded,  toad-like 
caricature  of  humanity  may  be  restored  to 
mental  and  bodily  health.  The  skin  becomes 
moist,  the  pulse  rate  quickens,  and  the  mental 
torpor  lessens."  Thus  thyroid  deficiency,  with 
all  its  sad  consequences  for  the  individual  and 
society,  can  be  largely  overcome  by  the  simple 
introduction  into  the  body  of  an  appropriate 
material  from  the  outside. 

But  man  is  not  only  open  to  troubles  from 
deficient  thyroids ;  he  may  also  suffer  from  the 
excessive  activity  of  these  glands.  In  the  dis- 
ease known  as  exophthalmic  goitre  the  patient 
is  nerved  up  to  a  high  pitch  of  excitement,  the 
eyes  protrude,  and  in  general  the  symptoms 
are  the  reverse  of  those  exhibited  by  cases  of 
deficient  thyroid.  This  state  can  be  more  or 
less  artificially  produced  by  excessive  thyroid 
feeding,  and  the  disease  thus  imitated,  as  well 
as  that  dependent  upon  deficient  thyroids,  is 
important  for  us  in  showing  how  essential  for 
our  welfare  and  efficiency  in  the  social  organ- 
ism is  the  proper  amount  of  that  hormone 


HORMONES  49 

which  is  produced  by  a  few  ounces  of  glan- 
dular tissue  in  our  necks. 

Another  important  set  of  organs  in  the  pro- 
duction of  hormones  are  the  adrenal  bodies. 
These  are  paired,  gland-like  bodies  situated 
in  the  fat,  one  at  the  anterior  margin  of  each 
kidney ;  hence  their  name.  Each  adrenal  body 
consists  of  an  outer,  firm,  yellowish  layer,  the 
cortex,  and  of  an  inner,  soft,  gray  or  brownish 
mass,  the  medulla.  Like  the  thyroid,  the  ad- 
renals are  unprovided  with  ducts.  As  already 
mentioned,  their  removal  from  an  animal  is 
invariably  followed  by  its  death  in  a  few  days 
or  even  hours.  They  have  long  been  known  to 
be  associated  with  an  obscure,  fatal  disease, 
known  as  "Addison's  Disease,"  which  is 
marked  by  the  appearance  of  bronze  patches 
upon  the  skin.  From  their  medullary  portion 
there  has  been  extracted  a  substance  variously 
named  epinephrin,  adrenin,  or  adrenalin,  and 
capable  of  producing  profound  bodily  changes. 
This  substance  is  apparently  normally  present 
in  the  blood  in  very  small  amounts.  If  a  strip 
of  intestine  is  placed  in  a  warm  oxygenated 
Kinger's  solution,  it  will  show  rhythmic  con- 
tractions. If,  now,  to  one  hundred  million 
parts  of  this  solution  only  one  part  of  adre- 


50       BIOLOGY  AND  SOCIAL  PROBLEMS 

nalin  is  added,  these  contractions  cease  and  the 
bit  of  intestine  relaxes.  On  the  basis  of  such 
observations  as  this,  it  has  been  estimated  that 
the  adrenalin  in  our  blood  is  normally  about 
one  in  two  hundred  millions. 

Adrenalin  has  been  isolated  and  is  well 
known  chemically.  It  has  in  fact  been  pro- 
duced synthetically.  It  is  important  as  a  means 
of  checking  hemorrhages  in  minor  surgery,  for, 
on  local  application,  it  quickly  brings  about  a 
constriction  of  the  walls  of  the  blood  vessels. 

No  one  knows  with  certainty  what  purpose 
the  small,  constant  amount  of  adrenalin  in  the 
blood  serves,  but  when  more  of  this  substance 
appears,  certain  profound  and  significant 
changes  occur.  These  changes  may  be  stated 
briefly  as  follows :  a  cessation  of  the  activities 
of  the  alimentary  canal ;  a  notable  shifting  of 
the  volume  of  the  blood,  from  the  abdominal 
organs,  to  the  lungs,  heart,  central  nervous 
organs,  and  limbs  ;  an  increased  cardiac  vigor, 
an  augmentation  of  the  sugar  content  of  the 
blood ;  a  hastening  of  its  power  to  coagulate ; 
and  a  rapid  recovery  of  muscle  from  the  con- 
dition of  fatigue.  At  first  sight  this  seems  to 
be  a  heterogeneous  assembly  of  physiological 
effects  such  as  might  constitute  a  formal  de- 


HORMONES  51 

scription  of  the  action  of  any  substance  on  the 
body.  But  such  is  not  in  reality  the  case.  As 
Cannon  has  pointed  out,  all  these  facts  gather 
around  a  central  condition  of  no  small  biolog- 
ical interest,  namely,  preparation  for  physical 
struggle.  The  cessation  of  abdominal  activity 
and  the  transfer  of  blood  to  the  lungs,  heart, 
nervous  system,  and  limbs  is  an  adjustment 
whereby  the  nutritive  fluids  are  concentrated 
in  regions  important  for  muscular  activity. 
Increased  cardiac  vigor  improves  the  circula- 
tion in  these  regions.  The  increase  of  sugar 
in  the  blood  adds  to  its  nutritive  value  for 
muscular  work.  The  quickened  coagulability 
serves  as  an  increased  safeguard  in  case  of 
injury.  And  the  improvement  in  recovery  of 
muscle  from  fatigue  lengthens  the  time  dur- 
ing which  an  animal  may  continue  a  struggle. 
Thus  all  the  changes  induced  in  the  body  by 
an  increase  of  adrenalin  in  the  blood  may  be 
regarded  as  emergency  measures  for  times  of 
intense  struggle.  It  is,  therefore,  entirely 
natural  to  find  that  the  extra  adrenalin  neces- 
sary for  all  these  changes  is  produced  by  the 
glands  whenever  the  animal  is  driven  into  a 
condition  of  fear,  rage,  or  pain.  These  nervous 
states  reflexly  excite  in  the  adrenal  bodies 


52       BIOLOGY  AND  SOCIAL  PROBLEMS 

such  a  production  of  adrenalin  that  the  con- 
ditions already  described  are  almost  immedi- 
ately present ;  in  other  words,  when  an  animal 
is  excited  to  fear  or  rage  or  subjected  to  phys- 
ical pain,  its  whole  neuromuscular  mechanism 
and  related  parts  are  thrown  into  a  condition 
most  favorable  for  vigorous  and  protracted 
response.  The  biological  significance  of  this 
set  of  relations  from  the  standpoint  of  the 
struggle  for  existence  must  be  clearly  evident, 
and  we  see  again  how  a  highly  complex  sys- 
tem of  organic  interrelations  can  be  developed 
on  a  principle  other  than  that  of  nervous 
control. 

Just  as  the  thyroid  and  the  adrenals  can 
exert  a  profound  influence  on  the  activities  of 
the  body  through  their  hormones,  so  the  sex- 
ual glands  can  effect  changes  in  a  like  manner 
and  quite  independently  of  their  usual  prod- 
ucts. This  subject  has  been  worked  upon 
recently  with  very  interesting  results  by  Stein- 
ach.  The  method  employed  by  this  investi- 
gator was  as  follows :  Young  male  rats  and 
guinea-pigs  were  first  castrated,  after  which 
the  ovaries  from  a  young  female  of  the  appro- 
priate species  were  grafted  under  the  abdom- 
inal skin  of  each  castrated  male.  The  animals 


After  Steiuach 

PLATE  I.    FEMINIZED  GUINEA-PIGS 

Fig.  1.  Normal  male  guinea-pig.    Fig.  2.  Feminized  male  guinea-pig.    Bw,  nipple ;  GP, 
glans  penis ;  Ov,  position  of  implanted  ovary  ;  Wh,  areola. 


HORMONES  53 

were  then  allowed  to  grow  to  maturity  and 
the  development  of  the  secondary  sexual  char- 
acters was  closely  watched.  (Plate  I.)  The 
implanted  ovaries,  even  though  simply  under 
the  skin,  grew  and  ripened.  None  of  these  ani- 
mals developed  male  secondary  sexual  charac- 
ters ;  the  male  external  genitalia,  for  instance, 
remained  immature,  and  the  body  assumed  the 
form  of  the  smaller  sex,  the  female.  The  growth 
of  hair  and  the  deposition  of  fat  were  in  the 
direction  of  the  female  type.  The  mammary 
glands,  the  nipples,  and  their  surrounding 
areolse  were  typically  female.  None  of  these 
animals  showed  the  characteristic  male  sexual 
excitability  even  in  the  presence  of  a  female 
in  heat.  They  very  commonly  did  exhibit  the 
"  tail  reflex  "  and  the  "  protective  reflex,"  both 
characteristics  of  the  female,  and  they  were 
sought  by  males,  though  of  course  ineffec- 
tively. Thus,  so  far  as  the  secondary  sexual 
characters  were  concerned,  a  male  animal  had 
been  converted,  both  structurally  and  func- 
tionally, into  a  female. 

When  in  a  very  young  male  animal  the 
testes  were  transplanted  from  one  region  to 
another,  development  was  seen  to  proceed 
along  normal  lines.  Such  an  animal  in  the 


£4       BIOLOGY  AND  SOCIAL  PROBLEMS 

course  of  time  assumed  all  the  male  secondary 
sexual  characteristics  and  exhibited  sexual 
desire.  On  examining  its  transplanted  testes, 
however,  it  was  found  that  all  the  reproduc- 
tive cells  had  disappeared  and  that  the  inter- 
stitial cells  had  crowded  in  and  taken  their 
place.  For  this  reason  it  is  believed  that  the 
hormones  which  are  given  out  by  the  repro- 
ductive glands,  and  which  serve  to  excite  the 
development  of  the  secondary  sexual  charac- 
teristics, are  not  the  products  of  the  germ  cells 
proper,  the  egg  cells  and  sperm  cells,  but 
come  from  the  interstitial  cells  which  are  in 
no  wise  concerned  with  reproduction. 

Enough  is  known  concerning  operations 
and  transplantations  in  the  human  being  to 
justify  the  conclusion  that  the  results  obtained 
by  Steinach  on  the  lower  mammals  will  be 
found  to  apply  with  full  force  to  man.  The 
complete  removal  of  the  ovaries  from  a  woman 
is  always  followed  by  a  premature  menopause. 
In  the  case  of  a  woman  who  had  been  for  two 
years  without  ovaries  and  who  during  that 
period  had  not  menstruated,  the  successful 
grafting  into  her  body  of  a  live  ovary  from 
another  woman  was  followed  by  a  return  of 
menstruation  and  sexual  desire.  The  profound 


HORMONES  55 

effect  of  castration  on  the  male  body,  as  seen 
in  the  eunuchs  of  the  East,  is  too  well  known 
to  require  comment.  All  these  instances  show 
that  the  effects  of  the  reproductive  hormones 
in  man  are  quite  as  profound  and  significant 
as  they  are  in  the  lower  mammals,  and  that 
in  time  we  may  expect  to  see  confirmation  in 
man  of  many  of  the  facts  already  ascertained 
for  these  lower  forms.  Not  only  is  this  to  be 
expected,  but  it  is  reasonable  to  suppose  that 
the  solution  of  some  of  the  social  questions 
with  which  human  civilization  is  beset  to-day 
may  well  be  formulated  on  the  basis  of  such 
observations  as  those  of  Steinach  already  al- 
luded to. 

In  fact,  one  of  the  important  social  problems 
turns  on  the  very  points  that  have  just  been 
discussed.  The  question  is  as  to  the  best 
method  to  be  employed  in  the  sterilization  of 
defective  males.  Two  general  lines  are  possi- 
ble, either  castration,  that  is  the  complete  re- 
moval of  the  reproductive  glands,  or  some 
such  operation  as  the  cutting  of  the  spermatic 
ducts  or  other  treatment  whereby  the  repro- 
ductive cells  are  eventually  destroyed.  Both 
methods  render  the  individual  incapable  of 
having  offspring,  but,  judging  from  Stein- 


56       BIOLOGY  AND  SOCIAL  PROBLEMS 

ach's  results  on  the  guinea-pigs  and  rats,  the 
first  would  probably  also  profoundly  change 
his  character,  in  that  among  other  things  he 
would  lose  sexual  desire,  whereas  the  second 
would  leave  him  much  the  same  as  he  had 
been  except  as  to  this  ability  to  form  sperm 
cells.  Thus,  depending  upon  what  society 
wished  as  a  result,  one  or  other  course  might 
be  adopted. 

Another  interesting  line  of  hormone  activ- 
ity of  broad,  biological  significance  is  that  of 
the  relation  of  the  mammalian  embryo  to  the 
mother.  It  is  well  known  that  as  the  mamma- 
lian embryo  matures  many  preparatory  changes 
take  place  in  the  maternal  body.  Prominent 
among  these  are  the  steps  taken  by  the  mam- 
mary glands  in  preparation  for  the  flow  of 
milk  which  must  be  in  readiness  for  the  young 
at  birth.  How  are  these  preparatory  changes 
initiated  ?  It  is  well  known  that  there  are  no 
nervous  connections  between  the  mother  and 
the  embryo,  and  if  the  latter  influences  the 
former  it  must  be  through  some  such  means 
as  hormones.  Working  upon  this  suggestion, 
Starling  and  Lane-Claypon  attempted  to  as- 
certain whether  in  the  rabbit  the  embryos 
gave  out  hormones  which  gradually  brought 


HORMONES  57 

the  mammary  glands  into  activity.  To  test  this 
hypothesis,  they  made  an  extract  from  a  num- 
ber of  rabbit  embryos  and  injected  this  sub- 
cutaneously  into  virgin  female  rabbits.  The 
result  of  this  treatment  was  that  the  mammary 
glands  of  these  rabbits  underwent  the  prepar- 
atory growth  that  would  have  been  character- 
istic of  them  had  there  been  a  real  pregnancy. 
Further  evidence  of  the  same  kind  is  furnished 
by  the  interesting  case  of  the  Blazek  sisters, 
to  quote  from  Howell.  These  twins  were  joined 
like  the  Siamese  twins;  they  had  a  common 
circulation  but  separate  nervous  systems.  Preg- 
nancy and  parturition  in  one  was  followed 
by  a  secretion  of  the  mammary  glands  of 
both.  Thus  it  seems  quite  clear  that  the  devel- 
oping mammalian  embryo  gives  out  hormones 
to  the  maternal  body  and  that  these  hormones 
excite  activity  in  those  maternal  organs  which 
are  to  serve  the  young  after  birth.  It  would 
be  superfluous  to  point  out  here  the  signifi- 
cance of  these  relations  to  the  practice  of 
dairying.  In  my  opinion  a  step  has  been  taken 
in  the  laboratory  which  when  properly  fol- 
lowed up  may  revolutionize  our  methods  of 
dealing  with  the  milch  cow.  The  time  may 
not  be  very  distant  when  an  extract  of  calf 


5*       BIOLOGY  AND  SOCIAL  PROBLEMS 

may  be  more  generally  effective  than  the 
bull. 

Even  from  what  is  known  at  this  early 
stage  in  the  study  of  hormones,  it  must  be  evi- 
dent that  they  are  most  important  substances 
for  the  correlation  of  one  part  of  the  body 
with  another,  and  that  in  certain  instances 
they  may  rival  though  they  never  equal  in 
importance  nervous  methods  of  correlation. 
Of  course  the  whole  plan  of  hormone  interre- 
lation is  such  that  nothing  can  be  expected 
to  spring  from  it,  as  the  higher  nervous  func- 
tions have  grown  from  the  simpler  nervous 
operations ;  but,  from  the  instances  cited,  it 
must  be  clear  that  next  to  the  nervous  system 
nothing  will  be  found  so  potent  for  the  con- 
trol of  animal  activity  as  the  hormones. 

In  much  of  the  preceding  account,  I  have 
dealt  with  the  nervous  system  and  the  hor- 
mones as  though  they  were  distinct  arid  sep- 
arate means  of  accomplishing  very  similar 
ends.  But  as  might  be  suspected  by  any  one 
who  is  conversant  with  the  conditions  in  organ- 
isms, both  means  are  often  most  complexly 
and  intricately  interwoven  in  the  perform- 
ance of  a  single  act.  This  is  well  illustrated 
in  our  respiration.  Nothing  seems  simpler  or 


HORMONES  59 

easier  than  the  regular  filling  and  emptying 
of  our  lungs  with  air,  and  yet  the  operation 
is  carried  on  in  a  way  that  illustrates  prac- 
tically all  the  forms  of  nervous  and  hormone 
action  of  which  I  have  spoken. 

The  muscles  concerned  with  the  respiratory 
movements  are  those  of  the  lower  neck,  the 
chest,  and  the  upper  abdomen.  They  are  con- 
trolled from  a  pair  of  centers  closely  connected 
and  lying  in  the  midst  of  the  medulla  oblon- 
gata.  Although  these  centers  can  be  influ- 
enced from  almost  any  part  of  the  central 
nervous  system,  they  will  continue  to  give 
out  impulses  to  respiratory  movements  even 
after  they  have  been  separated  from  practi- 
cally all  afferent  tracts.  This  independence  of 
afferent  control  has  led  to  the  conclusion,  well 
supported  from  other  directions,  that  the  res- 
piratory centers  are  stimulated  by  the  quality 
of  the  blood  that  passes  through  them.  It  has 
been  shown  that  when  the  blood  that  reaches 
them  is  very  impure,  their  action  results  in 
vigorous  breathing,  and  that  when  it  is  more 
nearly  pure,  they  subside  in  their  activity  or 
even  cease  altogether.  The  constituent  of 
the  blood  which  is  effective  in  this  respect 
seems  to  be  the  carbon  dioxid,  and,  as  this  is 


60       BIOLOGY  AND  SOCIAL  PROBLEMS 

produced  in  many  parts  of  the  body,  it  may  be 
)  regarded  as  the  hormone  for  the  respiratory 
centers.  Thus  a  somewhat  regulated  interaction 
between  the  amount  of  carbon  dioxid  in  the 
blood  and  the  activity  of  the  respiratory  mech- 
anism takes  place,  in  that  with  an  increase  of 
carbon  dioxid  comes  an  increase  in  the  activity 
of  the  respiratory  mechanism  whereby  the  or- 
ganism is  relieved  of  this  excess  of  waste.  Thus 
an  equilibrium  between  the  amount  of  carbon 
dioxid  and  the  efficiency  of  respiratory  move- 
ment is  quickly  established. 

But  the  respiratory  rhythm  is  not  one  de- 
pendent simply  upon  carbon  dioxid.  The  lungs 
are  supplied  with  afferent  nerve  fibers  which 
make  their  way  to  the  central  organs  through 
the  vagus  nerves,  and  when  these  nerves  are 
cut  the  respiratory  movements  are  consider- 
ably changed,  becoming  slower  and  deeper. 
Under  normal  conditions  a  given  respiratory 
movement  apparently  stimulates  these  afferent 
fibers  in  such  a  way  that  they  bring  about  in 
a  purely  reflex  fashion  a  hastening  of  the  next 
response.  Thus  this  reflex  mechanism  has  a 
marked  influence  on  the  respiratory  rate. 

Although  the  respiratory  movements  ordi- 
narily proceed  without  relation  to  voluntary 


HORMONES  61 

operations,  we  know  that  within  a  certain 
range,  we  can  alter  them  to  suit  our  will. 
They  may  be  hastened,  or  slowed,  or  stopped 
altogether,  though  not  indefinitely;  in  other 
words,  they  are  more  or  less  voluntary.  The 
respiratory  movements  then  include  not  only 
hormone  control,  but  reflexes  of  the  simplest 
class  and  willed  actions,  a  range  which,  as  I 
intimated  before,  involves  almost  every  form 
of  control  known  in  the  body. 

The  fact  that  hormone  action  is  often  com- 
bined with  nerve  action  brings  us  face  to 
face  with  the  ancient  doctrine  of  the  humors. 
These  were  supposed  to  determine  personality 
in  a  way  already  indicated.  Many  substances 
produced  in  the  body,  though  not  specifically 
hormones,  may  affect  our  cerebral  cortex  in 
such  a  manner  as  to  color  our  whole  lives,  in 
fact  determine  our  temperaments.  We  all  rec- 
ognize the  passing  effect  of  tea,  coffee,  or  al- 
cohol. When  these  materials  are  not  taken  in 
sufficient  quantities  to  prove  poisonous,  they 
serve  as  intellectual  alteratives,  and  the  tem- 
porary condition  called  forth  by  them  leads 
us  to  suspect  that  the  naturally  vivacious  or 
taciturn  person  may  have  within  him  a  spring 
that  generates  unceasingly  the  appropriate 


62       BIOLOGY  AND  SOCIAL  PROBLEMS 

humor.  Every  one  is  familiar  with  the  feeling 
of  utter  exhaustion  after  protracted  strenuous 
physical  exercise.  Probably  most  of  you  know 
that  if  the  blood  of  a  dog  in  this  state  of 
overwork  is  transfused  into  the  body  of  a 
rested  dog,  the  second  animal  shows  all  the 
signs  of  lassitude  that  the  first  one  did.  Thus 
excessive  muscular  exercise  must  change  the 
composition  of  the  blood  in  such  a  way  that 
when  it  acts  upon  the  conscious  centers,  it 
generates  those  vague  sensations  that  we  de- 
scribe as  utter  tiredness,  a  condition  which  can 
be  easily  interpreted  from  the  standpoint  of 
the  hormones.  These  substances,  then,  not 
only  interrelate  distant  parts  and  activities  of 
the  human  body  as  in  its  simpler  phases  the 
nervous  system  does,  but  they  play  the  part 
of  the  ancient  humors,  and  color  momentarily 
or  even  permanently  that  aspect  of  our  nerv- 
ous systems  which  we  call  temperament. 


Ill 

KEPRODUCTION 

REPRODUCTION  is  one  of  the  most  charac- 
teristic and  fundamental  activities  of  living 
things.  Almost  every  organism,  plant  or  an- 
imal, possesses  this  power  during  some  period 
in  its  life.  In  a  few  instances  it  is  lacking,  as, 
for  example,  in  the  worker  bee,  a  sterile  fe- 
male, but  in  the  vast  majority  of  plants  and 
animals  it  is  characteristically  present.  Every 
species  must  contain  at  least  certain  individu- 
als concerned  with  this  function,  else  the  spe- 
cies would  become  extinct. 

The  methods  by  which  reproduction  is  ac- 
complished are  extremely  diverse.  In  the  sim- 
pler instances  the  fully  grown  body  of  one 
individual  divides  into  two  and  thus  produces 
material  for  two  new  individuals.  Examples 
of  this  kind  occur  among  the  unicellular  an- 
imals and  the  simpler  multicellular  forms 
such  as  the  corals,  worms,  and  the  like.  The 
more  complex  methods  of  reproduction  are 
accomplished  by  means  of  two  kinds  of  cells, 


64       BIOLOGY  AND  SOCIAL  PROBLEMS 

and  these  are  usually  produced  by  different 
individuals.  Individuals  that  produce  sperm 
cells  are  called  males,  those  that  produce  egg 
cells,  females.  The  production  of  a  new  indi- 
vidual is  initiated  as  a  rule  by  the  f usion  of 
a  sperm  cell  from  one  individual  with  an  egg 
cell  from  another.  For  obvious  reasons  this 
method  of  reproduction  is  designated  as  sex- 
ual in  contrast  with  non-sexual  reproduction, 
which  is  the  term  used  for  the  simpler  type. 

Sexual  reproduction  is  the  common  method 
of  increase  among  the  multicellular  animals, 
especially  the  more  complex  forms,  but  it  can- 
not be  said  to  be  entirely  absent  from  the 
unicellular  organisms.  In  man  reproduction  is 
accomplished  almost  exclusively  by  the  sexual 
/*  method,  there  being  only  a  few  somewhat  ob- 
*scure  and  rare  occurrences  that  can  be  inter- 
preted otherwise. 

When  we  reflect  on  the  enormous  struc- 
tural complexity  of  the  human  body,  its  count- 
less myriads  of  cells  appropriately  disposed  to 
form  its  organs,  and  particularly  when  we 
attempt  to  realize  the  immense  variety  of  proc- 
esses which  go  on  within  it,  many  of  which 
are  essential  to  its  continuance,  it  seems  as 
though  a  reproduction  of  such  a  complex 


REPRODUCTION  65 

would  be  open  to  so  many  accidents  and 
fraught  with  such  difficulties  as  to  be  well-nigh 
impossible.  And  yet,  with  every  well-born 
child  that  comes  into  the  world,  this  is  accom- 
plished. But  a  human  being  is  vastly  more 
than  a  successfully  adjusted  complex  of  cells 
whose  activities  are  sufficiently  intricate  and 
adaptable  to  meet  with  success  the  ever-chang- 
ing conditions  around  it.  A  human  being  is 
a  vast  sum  of  conscious  past  experience,  a 
longing,  desiring  creature  that  seeks  to  mold 
the  future,  a  dreamer  in  hours  of  wakef ulness, 
a  thing  of  affections  and  feelings.  And  this 
side  of  man's  nature,  too,  is  reproduced. 
But  by  what  process  ?  As  in  former  cases  we 
shall  attack  this  problem  from  its  material 
side.  What  are  the  physical  conditions  under 
which  reproduction  is  accomplished  ? 

William  Harvey,  the  discoverer  of  the  cir- 
culation of  the  blood,  in  his  treatise  on  gen- 
eration published  in  1651,  maintained  that 
"  even  on  the  same  grounds,  and  in  the  same 
manner  and  order  in  which  a  chick  is  engen- 
dered and  developed  from  an  egg,  is  the  em- 
bryo of  viviparous  animals  engendered  from 
a  preexisting  conception."  This  "  preexisting 
conception"  was  in  Harvey's  mind  the  exact 


66       BIOLOGY  AND  SOCIAL  PROBLEMS 

equivalent  of  an  egg  and  justified  the  phrase 
used  in  the  earlier  part  of  his  treatise  and  so 
often  associated  with  his  name,  "  Omne  vivum 
ex  ovo,"  every  living  thing  from  an  egg.  To 
this  declaration,  as  Harvey  explicitly  states, 
the  human  being  is  no  exception.  But  it  was 
not  vouchsafed  to  Harvey  to  see  the  egg  of 
man  or  of  any  other  viviparous  animal  except 
dimly  in  his  mind's  eye. 

The  egg  of  the  mammal  was  discovered  late 
in  the  spring  of  1827  by  Von  Baer.  The  first 
egg  seen  was  that  of  a  dog,  but  subsequently 
the  eggs  of  other  mammals,  including  man, 
were  found,  and  an  account  of  the  whole  re- 
search was  published  in  the  latter  part  of  that 
year.  This  matter-of-fact  statement  of  an  in- 
vestigation, the  repetition  of  which  would  be 
a  simple  affair  in  the  hands  of  even  an  elemen- 
tary student  to-day,  gives  no  idea  of  what  it 
cost  its  discoverer.  In  his  autobiography  Von 
Baer  speaks  of  the  physical  strain  and  damage 
to  health  from  the  long  hours  he  spent  over 
his  microscope  and  his  worktable,  and  because 
of  his  reluctance  to  leave  his  workshop,  he  com- 
pares himself  to  a  hermit  crab.  "And  so  it 
happened,"  he  says,  "  that  in  the  course  of  a 
year,  I  shut  myself  up  in  my  shell  while  the 


REPRODUCTION  67 

snow  was  still  on  the  ground,  and  when  I 
again  ventured  out  to  cross  the  garden  wall 
only  a  hundred  steps  from  me,  I  was  as- 
tounded to  find  that  the  fields  of  rye  were  in 
the  ear."  This  is  the  application  and  energy 
that  brought  to  light  the  mammalian  egg. 
The  fact  is  a  commonplace  now,  but  let  us 
not  forget  that  it  took  a  genius  to  point  it  out 
to  us. 

The  human  egg  is  a  minute  spherical  body 
just  about  visible  to  the  unaided  human  eye. 
It  has  a  diameter  of  about  one  fifth  of  a  milli- 
meter. Aside  from  a  slight  envelope,  it  is  com- 
posed of  a  mass  of  protoplasm  containing  some 
fine  yolk  granules  and  a  spherical  nucleus 
whose  diameter  is  about  one  seventh  or  one 
eighth  that  of  the  whole  structure.  Thus  the 
human  egg,  like  that  of  many  other  animals, 
exhibits  all  the  characteristics  of  a  simple  cell. 

The  two  ovaries  of  a  woman  shortly  after 
the  onset  of  puberty  are  estimated  to  contain 
seventy-two  thousand  so-called  primitive  eggs, 
of  which,  it  is  believed,  not  more  than  about 
four  hundred  become  mature  and  are  dis- 
charged. These  mature  egg  cells  are  liberated 
with  more  or  less  regularity  over  the  period 
of  sexual  maturity.  This  is  ordinarily  from 


68       BIOLOGY  AND  SOCIAL  PROBLEMS 

about  the  fourteenth  to  the  fiftieth  year, 
though  the  fact  that  pregnancy  may  occur  as 
early  as  the  seventh  year  shows  that  occasion- 
ally puberty  begins  very  early.  As  a  rule  only 
a  single  egg  cell  is  discharged  from  the  ovary 
at  each  period  of  ovulation,  but,  as  the  con- 
dition of  multiple  births  shows,  there  may  pos- 
sibly be  as  many  as  seven  eggs  freed  at  once. 
Quintuplets  have  occurred  often  enough  to 
place  this  number  beyond  doubt,  and  there 
have  been  apparently  a  few  good  cases  of  sex- 
tuplets.  An  instance  of  seven  at  a  birth  is 
said  to  be  recorded  in  Hameln-an-der-Weser, 
in  Germany,  on  a  memorial  tablet  of  the  year 
1600,  and  this,  so  far  as  I  can  ascertain,  is  the 
largest  well-authenticated  number  of  children 
delivered  at  a  birth,  for  the  case  of  eight  re- 
ported in  1872  from  Trumbull  County,  Ohio, 
seems  on  good  authority  to  be  spurious.  Al- 
though, as  we  shall  see  presently,  there  is  good 
reason  to  believe  that  some  eggs  divide  in  a 
way  to  give  rise  to  more  than  one  child,  it  is 
likewise  well  established  that  many  multiple 
births  are  due  to  the  liberation  of  several  eggs; 
how  many  as  a  maximum  cannot  be  stated, 
but  from  the  cases  just  quoted  it  is  not  neces- 
sary to  assume  more  than  seven.  In  such  in- 


REPRODUCTION  69 

stances  the  total  number  of  eggs  discharged 
by  a  woman  in  the  course  of  her  life  would 
probably  be  several  times  four  hundred,  but 
the  ordinary  rule  seems  to  be  a  single  egg  at 
each  of  the  four  hundred  or  more  ovulations. 
You  are  probably  aware  that  the  discharge  of 
the  egg  is  supposed  to  take  place  periodically 
and  to  be  related  to  menstruation,  but  if  there 
is  an  exact  relation  between  these  events,  it 
has  yet  to  be  discovered. 

As  it  is  the  characteristic  of  the  female  to 
produce  egg  cells,  so  it  is  that  of  the  male  to 
produce  sperm  cells.  The  human  sperm  cell,  or 
spermatozoon,  as  it  is  commonly  called,  was 
discovered  in  1677  by  Hamm,  a  student  in 
Leyden,  whose  master,  Leeuwenhoek,  gave  an 
accurate  description  of  it.  In  man  each  sper- 
matozoon is  a  minute,  elongated,  lashlike  body, 
one  end  of  which  is  somewhat  enlarged.  The 
whole  has  some  resemblance  to  a  much  atten- 
uated tadpole.  Each  spermatozoon  measures 
ordinarily  about  one  twentieth  of  a  millimeter 
in  length,  or  roughly  a  quarter  of  the  diame- 
ter of  the  human  egg.  Its  enlarged  end  cor- 
responds to  the  nucleus  of  a  cell,  and  its  lash 
to  the  protoplasm,  so  that  the  spermatozoon, 
like  the  egg,  is  a  single  cell,  though  its  form 


70       BIOLOGY  AND  SOCIAL  PROBLEMS 

at  first  sight  is  not  so  suggestive  of  this  com- 
parison. 

The  testes  in  man  produce  spermatozoa 
more  or  less  continuously  from  the  beginning 
of  puberty,  at  about  the  fifteenth  year,  on  to 
old  age.  Spermatozoa  are  often  absent  in  old 
men,  but  they  have  been  found  in  individuals 
as  late  as  the  ninetieth  year.  It  has  been  esti- 
mated that  in  the  period  of  thirty  years  be- 
tween the  twenty-fifth  and  the  fifty-fifth  year 
of  manhood,  one  individual  will  produce  the 
prodigious  number  of  339,385,500,000  sper- 
matozoa, a  number  incredibly  large  compared 
with  the  egg  cells  probably  liberated  by  the 
normal  woman  during  her  sexually  active  life. 

When  the  human  egg  cell  is  fully  formed, 
it  is  discharged  on  the  surface  of  the  ovary, 
whence  it  makes  its  way  down  the  Fallopian 
tube  toward  the  uterus  and  the  exterior.  If  it 
is  not  fertilized,  it  disintegrates  and  is  lost, 
but  if  copulation  has  occurred  and  sperm  cells 
abound  in  the  tube,  one  may  enter  the  egg 
and  thereby  fertilize  it.  The  fertilized  egg  then 
passes  down  the  Fallopian  tube  into  the  uterus, 
where,  instead  of  disintegrating,  it  attaches  it- 
self and  develops  into  an  embryo  and  eventu- 
ally into  a  fully  formed  child. 


REPRODUCTION  71 

It  is  evident  from  these  brief  statements 
that  the  two  parents  supply  very  unequal 
amounts  of  material  to  the  offspring.  The 
father  contributes  merely  one  spermatozoon 
whose  volume  is  surely  not  over  50  cubic  micra 
or  thousandths  of  a  millimeter;  the  mother 
contributes  the  substance  of  the  egg  cell, 
which,  if  it  be  regarded  as  spherical  and  with 
a  diameter  of  150  micra,  would  have  a  volume 
of  1,767,150  cubic  micra,  or  over  35,000  times 
that  of  the  sperm  cell.  Not  only  is  this  true, 
but  the  mother  likewise  contributes  from  the 
substance  of  her  body  all  the  nourishment  that 
enables  the  diminutive  egg  to  grow  to  a  fully 
formed  babe.  Hence  the  material  of  the  child's 
body  is  vastly  more  maternal  than  paternal  in 
its  origin. 

Notwithstanding  the  disparity  between  the 
amounts  of  material  contributed  by  the  two 
parents  to  the  offspring,  it  is  well  established 
that  in  any  population  as  a  whole  the  children 
show  about  as  much  resemblance  to  the  father 
as  to  the  mother ;  in  other  words,  in  inheri- 
tance the  mother  has  no  more  influence  than 
the  father.  This  condition  has  led  to  a  closer 
scrutiny  of  the  actual  contributions  of  the  two 
parents. 


72       BIOLOGY  AND  SOCIAL  PROBLEMS 

The  mature  egg  about  to  be  fertilized  rep- 
resents all  the  material  of  maternal  origin  at 
this  early  stage  in  development.  This  mate- 
rial consists  of  the  protoplasm  of  the  egg  and 
of  certain  nuclear  bodies  called  chromosomes 
because  of  the  ease  with  which  they  become 
colored  in  artificially  stained  preparations. 
These  chromosomes  are  peculiar  in  that  they 
are  very  constant  in  number  for  the  eggs, 
sperm,  or  other  cells  of  a  given  animal.  In 
the  human  being,  because  of  the  unfavorable- 
ness  of  the  material  and  of  the  difficulty  in 
getting  it  in  a  well-preserved  condition,  the 
number  of  chromosomes  has  probably  not 
been  finally  determined.  According  to  the  re- 
searches of  Winiwarter,  published  in  the  last 
few  years,  the  number  of  chromosomes  in  the 
ordinary  cells  of  the  human  body  is  forty- 
seven  in  the  male  and  probably  forty-eight  in 
the  female.  As  just  intimated,  however,  these 
determinations  may  not  be  final,  but  whatever 
the  number  may  actually  prove  to  be,  it  is 
probably  not  far  from  what  has  just  been 
mentioned.  It  is  remarkable  that  in  practically 
all  animals  the  number  of  chromosomes  in  the 
mature  egg  cell  is  half  that  found  in  the  ordi- 
nary cells  of  the  body  of  the  female  for  the 


REPRODUCTION  73 

given  species.  Hence  in  man  we  would  expect 
the  number  of  chromosomes  in  the  mature  egg 
cell  to  be  twenty-four. 

In  the  operation  of  reproduction  the  father 
contributes  a  spermatozoon  which,  when  it 
enters  the  egg,  carries  with  it  a  negligible 
amount  of  protoplasm,  a  minute  body  called 
a  centrosome,  and  a  group  of  chromosomes 
essentially  like  those  from  the  mother,  and 
about  equal  to  them  in  number.  Thus  the  fer- 
tilized egg  consists  of  protoplasm  almost  en- 
tirely from  the  mother,  of  a  centrosome  from 
the  father,  and  of  chromosomes  in  about  equal 
numbers  from  each  parent.  If  children  always 
took  after  their  mother,  we  might  suspect  that 
part  of  the  fertilized  egg  which  came  exclusively 
from  the  maternal  side,  namely,  the  protoplasm, 
to  be  the  bearer  of  hereditary  traits.  If  they 
regularly  took  after  the  father,  we  might,  with 
equal  right,  suspect  the  centrosome  as  the 
organ  of  transmission.  But  as  children  take 
more  or  less  after  both  parents  and  as  the  only 
parts  of  the  fertilized  egg  which  are  derived 
from  both  sources  are  the  chromosomes, 
these  bodies  are  believed  to  be  the  means  by 
which  inheritance  is  accomplished.  If  this 
opinion  is  correct,  one  must  conclude  that  all 


74       BIOLOGY  AND  SOCIAL  PROBLEMS 

those  details  of  stature,  color  of  hair,  facial 
and  bodily  form,  inborn  acts,  and  other  traits 
that  make  the  child  resemble  the  parent  are 
dependent  upon  this  infinitely  small  amount 
of  living  substance  which  is  thus  handed  on 
from  parent  to  offspring.  Although  this  doc- 
trine is  not  without  its  opponents,  it  is  so  well 
substantiated  in  many  ways  as  to  have  gained 
very  general  credence. 

One  of  the  recent  lines  of  evidence  that 
supports  this  view  is  that  touching  on  sex  de- 
termination. From  the  most  ancient  times  the 
question  of  sex  has  been  one  of  great  theo- 
retical and  practical  interest,  and  many  hy- 
potheses have  been  advanced  and  advice  of 
all  kinds  has  been  sought  and  given  without 
resulting  in  any  evident  control  over  this  mat- 
ter in  either  man  or  the  lower  animals.  Many 
have  believed  that  the  resting  posture  of  the 
body  of  the  mother  during  pregnancy  or  the 
character  and  amount  of  the  food  given  her 
would  determine  the  sex  of  the  developing 
child.  But  all  such  theories  were  rendered 
very  improbable  by  the  occurrence  of  identi- 
cal twins,  triplets,  quadruplets,  and  so  forth. 
In  man  ordinary  twins  usually  have  separate 
sets  of  foetal  membranes  and  always  separate 


REPRODUCTION  75 

chorions.  They  give  every  evidence  of  having 
descended  separately  from  two  fertilized  eggs. 
They  may  be  of  the  same  or  opposite  sex. 
After  birth  they  resemble  each  other  no  more 
than  any  other  two  children  in  the  same  fam- 
ily. Identical  twins,  on  the  other  hand,  possess 
only  one  chorion  and  are  otherwise  so  related 
to  their  fcetal  membranes  as  to  give  evidence 
that  they  have  descended  from  a  single  egg. 
They  are  invariably  of  the  same  sex,  and  in 
after  life  they  are  commonly  very  similar  in 
appearance.  This  similarity  is  often  so  marked 
as  to  lead  to  their  confusion  even  among  their 
near  associates ;  hence  the  ludicrous  situations 
furnished  by  the  two  Dromios  and  their  mas- 
ters in  "  Comedy  of  Errors  "  as  well  as  by  their 
classical  progenitors,  the  Menaechmi.  Identical 
twins  are  never  of  opposite  sex,  as  Viola  and 
Sebastian  in  "Twelfth  Night,"  who,  though 
"  born  in  an  hour,"  must  have  been  descend- 
ants from  separate  eggs,  if  not  the  pure  prod- 
uct of  a  poet's  imagination.  The  fact  that  iden- 
tical twins  are  always  of  the  same  sex,  and  that 
ordinary  twins  may  or  may  not  be,  shows 
that  sex  determination  must  be  an  operation 
that  occurs  in  the  very  early  stages  of  devel- 
opment and  before  the  material  ordinarily  des- 


76       BIOLOGY  AND  SOCIAL  PROBLEMS 

tined  to  give  rise  to  one  individual  divides  in 
the  case  of  identical  twins  into  two.  Therefore 
the  subsequent  history  of  the  embryo,  such  as 
the  position  afforded  it  in  the  mother's  body  or 
the  character  and  amount  of  nourishment  pro- 
vided for  it,  can  have  no  influence  on  its  sex. 
This  interpretation  of  the  condition  in  man 
is  abundantly  supported  by  recent  work  on 
one  of  the  primitive  mammals,  the  armadillo. 
It  was  long  ago  known  that  all  the  young  in 
a  single  litter  of  this  animal  were  of  the  same 
sex.  Newman  and  Patterson  have  recently 
shown  that  in  the  armadillo  only  one  egg  is 
discharged  from  the  ovary  at  each  period  of 
heat,  and  that,  if  this  egg  is  fertilized,  four 
embryos  usually  result,  all  of  the  same  sex. 
These  four  embryos,  to  use  Morgan's  state- 
ment of  the  case,  are  more  like  each  other 
than  like  the  embryos  of  any  other  litter,  or 
even  more  like  each  other  than  they  are  like 
their  own  mother.  In  other  words  they  are 
identical  quadruplets  exactly  comparable  to 
identical  twins  in  man.  The  fact  that  they  are 
always  of  the  same  sex  and  are  positively 
known  to  come  from  one  egg  cell  supports 
most  completely  the  conclusion  arrived  at 
from  the  study  of  human  twins. 


REPRODUCTION  77 

It  is  the  process  of  forming  two  or  more 
human  embryos  from  the  substance  of  one 
egg  that  has  given  color  to  the  statement  that 
man  does  exhibit  at  times  non-sexual  repro- 
duction, for  the  differentiation  of  two  or  more 
embryos  from  the  mass  of  cells  that  would 
ordinarily  produce  a  single  one  is  apparently 
a  process  of  budding,  and  in  this  respect  it  •  fa 
may  be  maintained  that  man  occasionally  re- 
produces non-sexually. 

But  this  aspect  of  identical  twins,  interest- 
ing as  it  may  be  to  the  philosophical  zoologist, 
is  of  much  less  significance  than  that  which 
touches  on  the  determination  of  sex.  This  oper- 
ation is  not  only  known  through  the  condi- 
tion in  identical  twins  to  be  associated  with  a 
very  early  stage  of  development,  but  evidence 
from  certain  lower  animals,  chiefly  the  insects, 
indicates  that  it  is  involved  in  the  very  earliest 
stages  of  the  differentiation  of  egg  cells  and 
sperm  cells.  This  is  well  illustrated  in  Pro- 
tenor  belfragei,  an  insect  closely  related  to  the 
squash  bug.  When  the  ordinary  cells  in  the 
body  of  the  female  of  this  insect  divide, 
the  number  of  those  peculiar  nuclear  bodies 
known  as  chromosomes  is  seen  to  be  fourteen. 
In  the  formation  of  the  egg  cells,  as  might  be 


I 

78       BIOLOGY  AND  SOCIAL  PROBLEMS 

expected,  these  chromosomes  become  reduced 
in  number  to  half  that  characteristic  of  the 
cells  of  the  body ;  in  other  words,  each  mature 
egg  cell  contains  seven  chromosomes.  When 
the  ordinary  cells  in  the  body  of  the  male  of 
this  insect  divide,  the  number  of  chromosomes 
is  seen  to  be  thirteen,  one  less  than  in  the 
female,  and  when  the  spermatozoa  in  this  ani- 
mal are  formed,  the  reduction  in  the  original 
number  of  thirteen  results  in  the  formation 
of  two  classes  of  sperm  cells,  one  with  seven 
chromosomes  and  the  other  with  six.  These 
sperm  cells  are  formed  in  equal  numbers  and 
are  apparently  the  means  of  sex  determina- 
tion. For,  when  an  egg  with  its  seven  chromo- 
somes is  fertilized  with  a  sperm  having  the 
same  number,  an  individual  arises  whose  body 
cells  exhibit  fourteen  chromosomes,  and  such 
animals  are  females.  When,  on  the  other 
hand,  an  egg  is  fertilized  by  a  sperm  with  only 
six  chromosomes,  an  individual  whose  body 
cells  contain  only  thirteen  chromosomes  re- 
sults, and  the  animal  is  a  male.  It  is  thus 
clear  that  in  this  instance  the  fertilizing  sper- 
matozoon determines  the  sex  of  the  offspring 
and  that  the  material  which  is  concerned  in 
this  is  that  contained  in  the  chromosome.  Not 


REPRODUCTION  79 

only  are  the  chromosomes  thus  concerned  with 
sex  determination,  but  from  the  fact  that  they 
possess  somewhat  different  forms,  there  is  rea- 
son to  believe  that  a  particular  chromosome  is 
responsible  for  this  determination.  Thus  in 
Protenor  an  especially  large  chromosome  is 
always  found  in  those  sperm  cells  that  have 
seven  such  bodies,  that  is,  in  those  that  pro- 
duce females,  and  it  is  as  regularly  absent 
from  those  that  produce  males.  Hence  this 
chromosome  is  sometimes  called  the  sex  chro- 
mosome. 

Sex  determination  from  the  point  of  view 
just  presented  has  been  studied  in  many  other 
animals  and,  though  the  process  presents  a 
great  variety  of  details,  it  seems  to  turn  reg- 
ularly on  the  chromosome  composition  of  the 
reproductive  cells.  In  man,  as  already  stated, 
the  reproductive  elements  are  not  so  favorable 
for  this  kind  of  study  as  in  many  other  ani- 
mals, but  within  a  few  years  Winiwarter  has 
shown  that  human  spermatozoa,  like  those  of 
Protenor,  are  probably  of  two  classes,  one 
characterized  by  the  presence  in  each  cell  of 
twenty-three  chromosomes  and  the  other  by 
twenty-four  such  bodies.  If  this  is  true,  sex 
determination  in  man  is  brought  about  prob- 


80       BIOLOGY  AND  SOCIAL  PROBLEMS 

ably  by  the  same  means  as  in  animals  like 
Protenor,  in  that  when  the  human  egg  is 
fertilized  by  a  sperm  with  twenty-three  chro- 
mosomes a  male  results  and  when  by  a  sperm 
with  twenty-four  chromosomes  a  female  is  the 
outcome.  If,  as  in  insects,  the  two  kinds  of 
spermatozoa  in  man  are  about  equally  numer- 
ous, we  can  understand  why  male  and  female 
human  births  are  so  nearly  equal  in  number. 

From  what  has  been  stated  concerning  the 
composition  of  the  fertilized  egg  and  the  na- 
ture of  sex  determination,  it  must  be  clear 
that  the  chromosomes  are  most  significant 
bodies  in  inheritance,  in  fact  they  seem  to  be 
the  vehicles  of  this  process.  The  reason  we 
inherit  from  our  two  parents  those  character- 
istics of  feature  and  action  which  mark  us  as 
their  descendants  is  because  they  have  each 
contributed  a  certain  number  of  chromosomes 
to  our  make-up. 

Simple  as  this  statement  is,  when  we  face 
the  full  actualities  of  the  case,  it  strains  even 
the  imagination.  That  so  small  an  amount  of 
material  as  that  represented  in  the  chromo- 
somes of  the  fertilized  egg  should  influence  in 
so  rigid  a  way  so  large  an  amount  as  that  con- 
tained in  the  adult  body  seems  almost  incredi- 


REPRODUCTION  81 

ble.  The  human  egg  is  approximately  a  sphere 
with  a  diameter,  in  the  case  of  a  large  exam- 
ple, of  about  one  fifth  of  a  millimeter,  and  with 
a  specific  gravity  about  that  of  water ;  conse- 
quently its  weight  must  be  about  0.004  of 
a  milligram.  The  volume  of  the  chromosomes 
in  a  fertilized  mouse  egg  has  been  determined 
to  be  somewhat  less  than  one  thousandth  of 
the  volume  of  the  whole  egg,  and,  assuming 
that  this  proportion  hold  for  the  human  egg, 
and  that  its  chromosomes  have  about  the  same 
specific  gravity  as  water,  the  weight  of  this 
material  would  be  about  0.000,004  of  a  milli- 
gram. Yet  this  minute  amount  of  substance 
is  believed  to  determine  to  a  nicety  that  infin- 
ity of  adult  traits  wherein  a  man  resembles 
his  parents.  If  we  assume  the  weight  of  the 
average  human  being  to  be  sixty-five  kilo- 
grams, then  the  weight  of  the  determining 
material  to  that  which  is  determined  is  as  1  to 
16,250,000,000,000.  In  attempting  to  grasp 
this  almost  inconceivable  relation,  it  must  be 
borne  in  mind  that  the  material  of  the  chromo- 
somes in  the  egg  is  living  and  that,  in  the 
growth  of  the  individual,  it  assimilates  and  in- 
creases in  volume  like  other  living  material ; 
it  is  not  spread  through  the  growing  body  in 


82       BIOLOGY  AND  SOCIAL  PROBLEMS 

ever  increasing  dilution.  Nevertheless  it  is  this 
extremely  minute  amount  of  material  in  the 
egg  cell  that  gives  rise  to  that  which  deter- 
mines in  the  adult. 

The  fullness  of  this  determining  power  is 
seldom  appreciated  for  the  reason  that,  in  or- 
dinary births,  we  have  nothing  as  a  standard 
whereby  to  judge  of  the  looseness  or  rigidity 
of  the  process  of  inheritance.  But  in  identical 
twins,  triplets,  and  so  forth,  one  individual  in 
each  group  may  be  taken  as  a  standard  for  the 
rest  in  the  group,  and  we  can  judge  from  the 
similarity  of  the  members  in  a  single  group 
how  closely  the  process  works.  Wilder  gives 
us  good  evidence  on  this  point  taken  from  a 
set  of  identical  triplet  girls  by  a  person  who 
was  familiar  with  them.  This  person  described 
them  in  the  following  terms :  "  I  have  seen 
twins  that  looked  very  much  alike,  but  I  could 
see  a  difference  when  they  were  together.  I 
could  not  see  any  difference  in  these  triplets 
when  they  stood  in  a  row  before  me,  and  I 
never  saw  any  one  else  who  could,  except  their 
mother.  She  said  she  could,  but  I  doubted  it ; 
they  used  to  fool  her  often.  When  they  were 
babies  she  kept  different  colored  beads  around 
their  necks  to  tell  them  by.  They  always 


REPRODUCTION  83 

weighed  on  the  same  notch  until  they  were 
seven  years  old,  then  one  gained  half  a  pound 
more  than  the  others."  When  they  were  little 
girls,  one  of  them  confided  one  day  to  a  friend 
that  she  had  been  bathed  three  times  that 
morning,  while  the  others  confessed  that  they 
had  not  been  bathed  at  all,  an  accident  that 
emphasized  their  complete  bodily  identity  at 
that  period.  Their  lives  must  have  been,  in- 
deed, a  modern  "  Comedy  of  Errors."  But  for 
us  they  are  significant  in  that  they  show  how 
enormously  powerful  in  determining  traits  was 
that  infinitesimally  small  amount  of  chromatic 
material  contained  in  the  one  microscopic  egg 
from  which  they  all  came,  a  power  which  when 
spread  through  three  persons  instead  of  one 
seems  still  to  be  undiminished.  But  we  must 
remember  that  the  human  body,  like  that  of 
many  other  animals,  is  often  very  sensitive  to 
minute  amounts  of  material.  Cats  are  known 
to  be  affected  by  0.0001  of  a  milligram  of  ad- 
renalin, and  our  olfactory  organs  are  stimu- 
lated by  0.000,000,002  of  a  milligram  of  mer- 
captan.  Is  it,  therefore,  after  all,  so  surprising 
that  0.000,004  of  a  milligram  of  chromatic 
material  should  have  so  profound  an  influence 
on  our  development  ?  Small  as  these  amounts 


84        BIOLOGY  AND  SOCIAL  PROBLEMS 

are,  they  are  far  from  molecular  limits,  for 
Von  Frey  has  calculated  that  the  extremely 
minute  amount  of  mercaptan  which  we  can 
just  smell  contains  ahout  a  fifth  of  a  billion  of 
molecules.  Nevertheless,  as  compared  with  the 
smallest  amount  of  material  that  the  physi- 
cist or  chemist  can  weigh  directly  and  accu- 
rately, namely,  about  0.001  of  a  milligram,  the 
amounts  of  the  various  materials  just  men- 
tioned are  undeniably  small. 

We  have  thus  seen  how  each  human  being 
starts  life  from  a  minute  egg  cell  charged  with 
an  infinitesimally  small  amount  of  material 
which  is  destined  to  determine  with  surprising 
accuracy  his  configuration  and  responsiveness. 
The  process  that  the  egg  cell  undergoes  in 
changing  into  an  adult  person  is  first  of  all 
cell  division.  The  simple  spherical  egg  cell  di- 
vides by  a  somewhat  complex  process  into  two 
cells,  and  these  into  four,  and  so  forth,  till 
the  millions  upon  millions  of  cells  which  con- 
stitute the  adult  body  are  formed.  At  each  di- 
vision the  chromosomes  divide  and  are  shared 
by  the  descendant  cells  so  that  both  maternal 
and  paternal  influences  are  handed  on  to  each 
cell  in  the  growing  individual.  The  great  ag- 
gregate of  cells  which  thus  constitute  the  adult 


REPRODUCTION  85 

body,  and  which  are  all  descendants  from  the 
single  original  egg  cell,  falls  naturally  into  two 
classes ;  first,  somatic  cells,  such  as  those  which 
form  the  skin,  muscles,  bone,  nerve,  and  other 
parts  of  the  adult  body,  and,  secondly,  the  re- 
productive cells,  the  egg  cells  in  the  female 
and  the  sperm  ceUs  in  the  male,  which  are  des- 
tined to  give  rise  to  new  individuals.  Of  these 
two  sets  of  cells  the  one  which  by  its  collective 
arrangement  and  activity  exhibits  those  as- 
pects of  the  child  wherein  it  shows  its  likeness 
to  its  parents  are  the  somatic  cells,  and  the 
discovery  of  the  way  in  which  these  cells  be- 
come impressed  with  the  parental  traits  is  one 
of  the  chief  problems  of  genetics. 

Before  1900  scarcely  anything  of  value  in 
genetics  could  be  said  to  have  been  in  the 
hands  of  the  working  biologist,  but  with  that 
year  the  discovery  of  Mendel's  writings,  lost 
for  about  a  generation,  gave  to  the  study  of 
heredity  such  an  impetus  as  it  had  never  ex- 
perienced before.  The  Mendelian  principles, 
to  which  this  revival  is  due,  are  already  popu- 
larly known.  You  are  aware  that  inheritance 
in  accordance  with  these  principles  is  accom- 
plished by  the  association  of  characteristics  re- 
lated in  pairs  and  that  these  characteristics 


80       BIOLOGY  AND  SOCIAL  PROBLEMS 

appear  in  the  offspring  unmixed  and  in  highly 
significant  proportions.  Thus  in  guinea-pigs 
the  white  coat-color  of  a  pure  albino  stock 
and  the  black  coat-color  of  a  pure  melanic 
stock  can  be  made  to  associate  by  crossing 
these  two  stocks.  The  animals  that  result 
from  this  cross  are  not,  as  you  well  know,  gray 
individuals  midway  between  the  white  and 
black  parents,  but  all  strictly  black  individ- 
uals to  all  appearances  like  their  black  an- 
cestor. That  they  are  not,  however,  exactly 
like  this  ancestor  is  seen  from  the  fact  that 
when  they  are  bred  among  themselves,  in- 
stead of  producing  nothing  but  black  indi- 
viduals as  their  black  parent  would  have  done 
if  mated  with  his  kind,  they  bring  forth  pure 
white  stock  as  well  as  black  stock  and  in  the 
proportion  of  one  of  the  former  to  three  of 
the  latter.  Thus  these  black  individuals  can 
be  shown  to  carry  hidden  in  their  bodies  the 
white  characteristic,  though  they  show  noth- 
ing of  this  on  their  exteriors.  Of  such  pairs 
of  characteristics,  the  one  which  may  thus  be 
hidden  is  spoken  of  as  recessive,  the  other 
dominant.  (Plate  II.) 

The  black  and  the  white  descendants  of 
such  individuals  occur  in  the  very  remarkable 


All  figures  after  Castle 

PLATE  II.    MENDELIAN   INHERITANCE 

Fig.  1.  A  black  female  guinea-pig.  Fig.  2.  An  albino  male  guinea-pig.  Fig.  3.  A  black 
female  guinea-pig  with  young  by  an  albino  male  such  as  that  shown  in  Fig.  2.  Fig.  4. 
Adult  black  guinea-pigs  from  a  litter  such  as  that  shown  in  Fig.  3.  Fig.  5.  Albino  and 
black  guinea-pigs  whose  parents  are  shown  in  Fig.  4. 


REPRODUCTION  87 

proportions  just  mentioned  and  present  con- 
ditions of  great  interest.  The  twenty-five  per 
cent  of  white  individuals,  when  bred  among 
themselves,  have  been  proved  to  be  pure  whites 
like  their  white  grandparent.  The  seventy- 
five  per  cent  of  black  individuals,  when  tested 
in  a  like  fashion,  have  been  shown  to  be,  in 
the  case  of  twenty-five  per  cent,  pure  black  like 
their  black  grandparent,  and,  in  the  case  of 
the  remaining  fifty  per  cent,  black  but  with 
the  ability  to  produce  white  offspring  exactly 
as  their  parents  did.  Thus  the  grandchildren 
of  the  original  pure  black  and  white  mating 
fall  into  three  classes:  twenty-five  per  cent  - 
pure  white,  twenty-five  per  cent  pure  black ;  ? 
and  fifty  per  cent  black,  but  capable  of  pro- 
ducing a  definite  proportion  of  white  off- 
spring. 

You  are  familiar  with  the  explanation  that 
Mendel  offered  lor  this  remarkable  state  of 
affairs,  an  explanation  that  is  still  generally 
accepted.  Briefly  it  is  to  the  effect  that  each 
reproductive  element,  egg  cell  or  sperm  cell, 
can  carry  only  one  of  any  pair  of  characteris- 
tics, and  that  in  this  respect  each  reproduc- 
tive cell,  be  it  either  egg  or  sperm,  is  pure. 
If  we  assume  this  segregation  of  characteris- 


88       BIOLOGY  AND  SOCIAL  PROBLEMS 

tics  together  with  the  principle  of  dominance, 
we  shall  find  it  easy  to  understand  the  condi- 
tions just  mentioned  for  the  guinea-pig. 

In  the  original  pair  of  animals  for  such  a 
series  of  breeding  experiments  as  have  been 
briefly  mentioned,  it  makes  no  difference  how 
the  sexes  are  combined;  the  male  may  be 
white  or  black,  the  outcome  will  be  the  same. 
But  for  simplicity  we  may  assume  that  the 
male  is  black  and  the  female  white.  As  each 
individual  comes  from  a  pure  stock,  the  male 
will  produce  sperm  cells,  all  of  which  will  carry 
the  black  characteristic,  and  the  female,  for 
the  same  reason,  will  produce  egg  cells,  all 
of  which  will  carry  the  white  characteristic. 
Their  offspring,  then,  will  be  the  product  of 
a  white  egg,  so  to  speak,  fertilized  by  a  black 
sperm.  Such  animals,  as  is  well  known,  are  al- 
ways black  in  color.  But  as  already  indicated 
they  possess  within  them  the  recessive  white 
characteristic.  If  we  assume,  now,  that  their 
reproductive  elements  are  pure  like  those  of 
their  parents,  then  we  should  expect  each  male 
of  this  stock  to  produce,  not  one  kind  of  sperm, 
but  two,  one  with  the  white  characteristic  and 
the  other  with  the  black,  and  that  these  ele- 
ments would  be  present  in  equal  numbers.  The 


REPRODUCTION  89 

same  would  hold  true  of  the  females ;  each  one 
would  give  rise  to  equal  numbers  of  black 
eggs  and  of  white  eggs. 

If,  now,  we  imagine  these  two  kinds  of  eggs 
to  be  fertilized  by  the  two  kinds  of  sperm  and 
that  the  combinations  be  purely  fortuitous,  we 
would  expect  four  classes  of  fertilized  eggs  of 
equal  frequency ;  once  in  four  a  white  egg 
would  be  fertilized  by  a  white  sperm,  once  in  X  ( 
four  a  black  egg  by  a  black  sperm  ;  once  in  ^  f 
four  a  black  egg  by  a  white  sperm ;  and  once  4J 
in  four  a  white  egg  by  a  black  sperm.  The 
first  class  would  yield  the  twenty-five  per  cent 
of  pure  white  individuals,  the  second  the  same 
per  cent  of  pure  black  individuals,  and  the 
third  and  fourth  the  fifty  per  cent  of  black 
individuals  which  are,  however,  capable  of 
producing  white  as  well  as  black  offspring. 
Thus  the  assumption  of  the  purity  of  the 
germ,  the  segregation  of  characteristics,  makes 
clear  these  very  remarkable  proportions  as 
seen  in  the  actual  experiments  in  heredity. 

The  conception  of  the  hereditary  proc- 
ess which  has  grown  out  of  this  idea  and 
the  way  in  which  this  process  is  supposed 
to  have  impressed  itself  upon  the  face  of 
nature  is  well  seen  in  the  mutation  theory 


90       BIOLOGY  AND  SOCIAL  PROBLEMS 

of  De  Vries.  According  to  De  Vries  the 
significant  hereditary  differences  between  in- 
dividual organisms,  plants  as  well  as  animals, 
depend  upon  the  presence  of  unit  characters, 
so  called,  such  as  those  of  black  or  white  coat- 
color  in  the  example  of  Mendelian  inheritance 
just  described.  These  unit  characters  were  be- 
lieved by  De  Vries  to  be  of  a  stability  com- 
parable with  that  of  the  chemical  elements ; 
there  were  no  intergrades.  Many  of  these 
unit  characters  are  known,  and  every  individ- 
ual organism  can  be  regarded  as  a  special 
combination  of  them.  Thus  animals  and  plants 
can  be  grouped  in  accordance  with  the  unit 
characters  that  enter  into  their  composition ; 
all  those  having  the  same  unit  characters  con- 
stitute what  De  Vries  calls  an  elementary 
species  and  when  they  differ  in  this  respect 
they  belong  to  different  elementary  species. 
Thus,  guinea-pigs  that  differ  in  coat-color, 
like  the  examples  previously  cited,  would  con- 
stitute two  elementary  species  separable  by 
the  specific  unit  characters  of  black  and  of 
white  coat-color.  It  is  to  be  observed  that  the 
conception  of  elementary  species  is  quite  dif- 
ferent from  that  of  the  old  LinnaBan  species. 
Two  members  of  the  same  elementary  species, 


REPRODUCTION  91 

such,  for  instance,  as  two  black  guinea-pigs, 
may  produce  offspring  some  of  which  may  be 
black  and  some  white.  In  other  words,  mem- 
bers of  one  elementary  species  may  have  in 
their  immediate  offspring  members  of  other 
elementary  species.  Thus  the  idea  of  contin- 
uity of  breed,  usually  attached  to  the  defi- 
nition of  a  Linnaan  species,  is  quite  absent 
from  that  of  the  elementary  species.  But  the 
main  fact  that  underlies  the  whole  De  Vriesian 
conception  is  the  fixity  of  unit  characters. 
That  there  is  a  large  body  of  truth  in  this,  for 
certain  characters  at  least,  cannot  be  denied, 
but  that  the  difference  is  comparable  with 
that  between  chemical  elements,  as  originally 
claimed  by  De  Vries,  is  far  from  probable. 
Evidence  on  this  point  comes  from  a  number 
of  sources,  but  I  shall  cite  only  one  instance. 
The  hooded  rat  is  a  domesticated  form  in 
which  the  fur  is  dark  over  the  head  and  down 
the  middle  of  the  back,  but  is  otherwise  light- 
colored.  Thus  the  rat  has  the  appearance  of 
a  light  animal  wearing  a  dark  hood.  When 
this  stock  is  crossed  with  the  uniformly  dark 
wild  rat,  the  hooded  character  is  found  to  be- 
have as  a  Mendelian  recessive ;  that  is,  in  the 
first  generation  of  descendants  all  individuals 


92       BIOLOGY  AND  SOCIAL  PROBLEMS 

have  the  coat-color  of  the  wild  parent,  but 
of  their  progeny  one  fourth  show  the  mark- 
ings of  the  hooded  stock.  This  hooded  char- 
acter, then,  is  what  may  be  called  a  unit  char- 
acter. 

Castle  has  attempted  to  ascertain  whether 
this  unit  character  can  be  modified  by  a  proc- 
ess of  selection,  the  object  being  to  produce 
from  the  hooded  stock  by  selection  two  ex- 
treme conditions  :  a  completely  light  animal, 
and  a  completely  dark  one.  In  the  beginning 
there  were  selected  from  the  common  hooded 
forms,  two  sets  of  individuals :  one  with  as 
little  pigmentation  as  possible,  the  other  with 
as  much.  These  two  sets  afforded  the  mate- 
rial with  which  the  test  began.  Their  descend- 
ants were  selected  in  the  desired  directions 
generation  by  generation  till,  after  somewhat 
more  than  six  years  of  work  on  over  twenty- 
five  thousand  rats,  two  clearly  divergent  stocks 
were  produced.  One  of  these  was  composed 
of  members  entirely  light  except  for  a  small 
amount  of  dark  on  the  head,  and  the  other 
was  made  up  of  individuals  completely  dark 
except  for  some  light  on  the  belly.  Thus  two 
stocks  were  obtained  that  bred  true  and  ap- 
proximated closely  to  the  two  extremes  aimed 


All  figures  after  Castle 

PLATE  III.    UNIT  CHARACTERS 

Fig.  1.  A  wild  gray  rat.  Fig.  2.  A  hooded  rat  with  the  hood  much  reduced  by  selection. 
Fig.  3.  A  normal  hooded  rat.  Fig.  4.  A  hooded  rat  with  the  hood  much  extended  by  selec- 
tion. Figs.  5  and  6.  Grandchildren  from  such  animals  as  those  shown  in  Figs.  1  and  2, 
which  they  respectively  resemble.  Their  parents  were  like  the  rat  shown  in  Fig.  1.  Figs. 
7  and  8.  Grandchildren  from  such  animals  as  those  shown  in  Figs.  1  and  4,  which  they 
respectively  resemble.  Their  parents  were  like  the  rat  shown  in  Fig.  1. 


REPRODUCTION  93 

at,  if  they  did  not  absolutely  arrive  there. 
(Plate  III.) 

Does  this  condition  indicate  that  the  unit 
character  of  the  original  hooded  stock  has 
gradually  been  pushed  along  in  one  derived 
stock  in  one  direction  and  in  the  other  in  the 
opposite,  or  is  this  whole  change  a  purely 
superficial  one  and  does  the  unit  character 
still  remain  in  both  stocks  unmodified?  An 
answer  to  this  question  was  found  by  cross- 
ing females  from  each  extreme  stock  with  a 
single  wild  dark  male  and  by  breeding  grand- 
children separately  from  each  of  the  two  sets 
of  descendants.  Under  such  circumstances  we 
should  expect  to  find  that  three  fourths  of 
the  grandchildren  of  both  sets  would  be  dark 
and  that  one  fourth  in  each  set  would  show 
the  condition  of  the  hooded  character.  Such 
proportions  were  practically  realized,  and  the 
hooded  individuals  in  the  two  sets  were  found 
to  be,  not  like  the  original  hooded  stock,  but 
like  their  modified  grandparents.  The  hooded 
individuals  from  the  light  grandmother  were 
mostly  light;  those  from  the  dark  grand- 
mother, mostly  dark.  These  results  show  that 
a  unit  character  is  not  necessarily  fixed,  as 
De  Vries  originally  maintained,  but  can  be 


94,       BIOLOGY  AND  SOCIAL  PROBLEMS 

modified  in  that  it  may  be  gradually  moved,  by 
selection,  for  instance,  in  one  direction  or  an- 
other. Marvelously  stable  as  the  unit  charac- 
ters are,  they  are  not  in  their  stability  com- 
parable with  the  chemical  elements,  for  they 
exhibit  gradual  changes.  Whether  these 
changes  are  to  be  accounted  for  on  the  basis 
of  inherited  modifiers,  a  kind  of  additional 
demon  behind  the  demon  unit  character,  or 
by  some  other  process,  is  a  question  for  the 
future  to  decide.  Of  one  point  we  can  feel 
fairly  certain,  unit  characters  are  modifiable. 
Although  these  results  have  been  worked 
out  almost  exclusively  on  the  smaller,  rapidly 
breeding  animals,  there  is  no  reason  to  sup- 
pose that  they  do  not  apply  with  full  force 
to  the  human  being.  Already  a  long  list  of 
characteristics,  which  are  inherited  in  man  in 
accordance  with  one  form  or  another  of  the 
Mendelian  principles,  is  known.  This  list  in- 
cludes certain  eye  colors ;  certain  hair  colors 
and  hair  forms,  such  as  straight,  wavy,  and 
curly ;  certain  skin  colors,  such  as  that  of  the 
blond  and  the  brunette ;  pale,  fresh,  and  col- 
ored complexions  in  the  white  race  ;  stature, 
form  of  head,  and  nose  in  certain  races ;  mu- 
sical and  non-musical  temperaments ;  various 


REPRODUCTION  95 

deformities  and  defects,  such  as  short  fingers, 
aborted  fingers,  split  fingers,  split  foot,  catar- 
act, certain  hair  deficiencies,  stationary  night- 
blindness,  certain  sex-limited  diseases  like 
haemophilia,  and  color-blindness ;  and  certain 
kinds  of  deaf-mutism,  insanity,  and  imbecil- 
ity. Thus  even  at  this  early  stage  in  the 
study  of  human  heredity,  there  is  good  reason 
to  believe  that  many  of  our  traits  Mendelize. 
But  the  question  that  confronts  the  modern 
student  of  genetics  is  the  extent  to  which 
Mendelism  may  be  said  to  apply.  Are  all 
characteristics  in  man  and  other  animals  in- 
herited in  accordance  with  these  principles,  or 
are  only  a  part  of  them  so  handed  on?  Man 
himself  seems  to  offer  some  very  interesting 
examples  that  are  very  difficult  to  bring  un- 
der the  Mendelian  rules.  Thus,  when  the  white 
man  is  crossed  with  the  negro  neither  one  nor 
the  other  is  produced,  but  an  intergrade,  the 
mulatto.  Inheritance  of  this  kind  is  called 
blended  and  is  represented  by  many  examples. 
Whether  it  is  a  form  of  Mendelism  in  which 
dominance  is  absent  is  not  clear.  Possibly  it 
is  a  totally  different  method  of  inheritance 
from  that  exemplified  in  the  Mendelian  cases. 
Certainly  so  long  as  instances  of  this  and  other 


96       BIOLOGY  AND  SOCIAL  PROBLEMS 

forms  of  inheritance  remain  unanalyzable  from 
the  Mendelian  standpoint,  we  may  conclude 
that  this  explanation  does  not  exhaust  the 
field  of  heredity.  But  even  if  Mendelism  is  an 
explanation  of  only  a  part  of  the  phenomena 
of  heredity,  it  represents  an  advance  in  all 
respects  the  most  important  that  the  science 
of  genetics  has  yet  made,  and  it  opens  up  a 
prospect  to  the  experimentalist  which  is  no 
less  alluring  than  it  is  full  of  promise. 

Notwithstanding  the  fragmentary  character 
of  our  knowledge  of  reproduction,  we  know 
that  a  child  takes  after  its  parents  because  the 
fertilized  egg  from  which  it  has  grown  is  made 
up  of  living  material  part  of  which  came  from 
each  immediate  ancestor.  The  amount  of  all 
the  material  in  the  egg  is  immensely  small 
compared  with  that  of  the  person  who  devel- 
ops from  it,  and  the  amount  of  that  material 
in  the  egg  concerned  with  heredity  is  probably 
not  over  a  thousandth  part  of  the  whole  egg ; 
nevertheless  this  infinitely  minute  quantity  of 
material,  rather  than  the  environment,  stamps 
upon  us  with  an  iron  hand  the  configuration 
of  our  early  life,  a  configuration  which  is  so 
rigidly  determined  that  where  two  or  more 
individuals  come  from  the  same  egg  almost 


REPRODUCTION  97 

complete  identity  results.  Yet  this  operation 
of  the  rigid  transfer  of  traits  from  individual 
to  individual  is  an  essential  step,  perhaps  the 
essential  step,  in  the  process  of  racial  progress- 
Without  it  the  evolution  of  man  would  have 
been  impossible.  In  the  last  lecture  I  shall  en- 
deavor to  show  the  relations  of  this  process 
of  reproduction  to  that  of  evolution  as  seen  in 
the  human  species. 


IV 

EVOLUTION 

ASSUMING  that  the  population  of  the  globe 
is  about  sixteen  hundred  millions  and  that  the 
average  length  of  human  lif e  is  forty  years,  a 
number  that  represents  the  present  condition 
in  only  the  more  favored  states  and  nations, 
about  forty  million  persons  must  die  annually. 
Of  such  persons  those  who  reach  maturity 
have  usually  gathered  about  them  material 
devices  as  protections  against  the  inclemen- 
cies of  nature  and  as  means  to  their  personal 
comfort.  Such  persons,  moreover,  in  the  course 
of  their  lifetime  develop  or  acquire  lines  of  ac- 
tion which  yield  continuance  of  life  and  hap- 
piness. At  their  death  their  material  property 
is  commonly  inherited  by  other  members  of 
society,  often  those  to  whom  the  deceased  had 
blood  ties ;  their  lines  of  action,  remembered 
or  otherwise  recorded,  serve  as  examples  for 
avoidance,  imitation,  or  improvement.  Thus, 
generation  by  generation,  the  composition  of 
human  society  changes,  its  material  acquisi- 


EVOLUTION  99 

tions  accumulate,  and  its  combined  forces  and 
activities  turn  now  this  way,  now  that.  We 
think  of  the  totality  of  these  changes  as  tak- 
ing place  through  a  process  of  evolution  by 
which  not  only  novel  features  arise,  but  the 
rich  inheritance  of  the  past  is  preserved  and 
handed  on.  When  we  reflect  on  the  means  by 
which  this  social  growth  is  accomplished,  we 
are  driven  to  admit  that  it  is  in  reality  the  indi- 
vidual man.  He  it  is,  who,  working  with  his  fel- 
lows, accomplishes  all.  What  he  inherits,  what 
he  devises,  what  he  can  hand  on,  these  are  the  3y 
elements  that  make  up  the  totality  of  social 
evolution.  Did  we  but  know  with  certainty 
how  all  this  change  comes  about,  many  of 
our  most  momentous  social  problems  would  be 
solved. 

To  many  naturalists  of  the  Darwinian  period 
an  experimental  laboratory  for  the  study  of 
evolution  would  have  seemed  to  be  resources 
thrown  away.  These  older  workers  supposed 
evolution  to  proceed  at  so  slow  a  pace  that  an 
experimental  investigation  of  it  would  be  im- 
possible, but  for  somewhat  over  a  decade  and 
mainly  in  consequence  of  the  discovery  of  Men- 
del's writings,  the  study  of  evolutionary  prob- 
lems from  the  experimental  standpoint  has 


100      BIOLOGY  AND  SOCIAL  PROBLEMS 

made  great  progress.  In  fact,  since  the  open- 
ing of  the  twentieth  century  a  more  substan- 
tial advance  has  been  made  in  the  solution  of 
evolutionary  questions  than  in  the  whole  pe- 
riod between  1859,  the  year  in  which  the 
"  Origin  of  Species  "  was  published,  and  1900. 

But  the  Darwinian  period  of  evolutionary 
activity  was  not  the  first.  It  was  preceded  by 
a  series  of  preliminary  skirmishes  fought  out 
mostly  upon  French  soil.  In  1809,  Lamarck, 
then  about  sixty-five  years  old,  published  his 
"Philosophic  Zoologique"  in  which  was  con- 
tained the  first  well-ordered  attempt  at  a 
general  theory  of  organic  evolution.  But  this 
fell  on  unsympathetic  ears.  It  was,  moreover, 
opposed  by  Cuvier,  whose  scientific  authority 
was  such  that  the  whole  movement  for  the 
time  being  was  swept  aside,  and  Lamarck,  in 
a  measure  unrecognized  and  after  an  old  age 
of  blindness,  died  in  1829. 

But  among  the  French  contemporaries  of 
Lamarck,  to  quote  freely  from  Delage,  was 
Etienne  Geoffroi  Saint-Hilaire.  He  it  was  who 
in  1830  took  his  stand  against  Cuvier  in  the 
Academy  of  Sciences  in  a  sensational  debate 
which  lasted  almost  six  months,  a  duel,  so  to 
speak,  between  the  theory  of  transmutation 


101 

and  the  theory  of  the  invariability  of  species. 
This  controversy  became  noised  throughout 
the  scientific  world.  Goethe,  then  eighty-one 
years  old,  took  a  keen  interest  in  it  and  de- 
voted his  last  work,  completed  in  1832,  to  a 
review  of  the  debate,  pointing  out  its  great 
scientific  and  philosophic  import.  Yet  the  out- 
come of  this  far-famed  contest  was  not  favor- 
able to  the  new  ideas.  In  the  opinion  of  the 
majority,  the  victory  remained  on  the  side  of 
Cuvier,  and  the  doctrine  of  transmutation  lost 
ground. 

The  general  theory  advanced  by  Lamarck 
contained  much  of  significance  and  impor- 
tance, and  was  in  part  accepted  by  Darwin.  In 
recent  years  it  has  been  revived,  at  least  in 
certain  particulars,  by  those  who  class  them- 
selves as  Neo-Lamarckians.  Lamarck  was  much 
impressed  by  what  he  believed  to  be  the  direct 
effects  of  the  environment  upon  organisms, 
particularly  plants,  and  he  attributed  evolution 
in  the  main  to  changes  in  this  factor.  His  idea 
of  the  way  in  which  animals  had  been  trans- 
formed was  through  what  might  be  called  the 
indirect  rather  than  the  direct  influence  of  the 
environment  and  may  be  briefly  stated  as  fol- 
lows :  changes  in  an  animal's  surroundings  in* 


lOfc     BIOLOGY  AND  SOCIAL  PROBLEMS 

duce  changes  in  its  habits,  and  changes  in  its 
habits  bring  about  changes  in  its  structure. 
Be  these  structural  changes  ever  so  slight,  if 
they  recur  regularly  from  generation  to  gen- 
eration and  are  accumulated,  they  will  even- 
tually so  modify  an  animal  that  a  transmu- 
tation of  species  may  be  said  to  occur.  Thus 
in  an  indirect  way  the  ever  changing  environ- 
ment is  responsible  for  animal  transformation. 

The  Lamarckian  hypothesis,  thus  stated, 
appeals  to  the  student  of  evolution  through 
its  simplicity  and  directness.  The  ease  with 
which  we  may  induce  modifications  in  our  own 
bodies  by  voluntary  change  of  habits  is  too 
well  known  to  require  comment.  The  special 
exercise  of  a  set  of  muscles  induces  an  increase 
in  their  size  and  that  of  all  their  connected 
parts,  and  the  reverse  of  this  is  followed  by 
their  shrinkage  and  decline.  What  could  be 
simpler  than  to  conceive  of  a  given  animal 
being  what  it  is  in  consequence  of  its  own  ac- 
tivities and  those  of  its  race  ?  Such  an  animal 
may  be  assumed  to  possess  its  present  form 
in  consequence  of  its  racial  habits. 

The  application  of  this  hypothesis  to  man 
is  most  readily  and  easily  accomplished,  and 
few  organisms  can  be  shown  to  afford  a  bet- 


EVOLUTION  103 

ter  apparent  example  of  its  mode  of  action 
than  the  human  species.  The  considerable  in- 
fluence that  the  kind  of  life  that  an  individual 
leads  has  upon  his  body  has  long  been  well 
recognized,  and  the  direct  effect  of  this,  fa- 
vorable or  unfavorable,  on  his  offspring  has 
underlain  the  claims  of  the  moralist  for  gen- 
erations past.  Thus  the  Lamarckian  hypothe- 
sis, though  an  impersonal  explanation  of  trans- 
mutation, can  be  easily  brought  into  relation 
with  man's  higher  nature  and  made  to  point 
a  moral. 

But  a  very  serious  obstacle  to  the  accept- 
ance of  this  hypothesis  has  gradually  arisen 
in  the  otherwise  easy  path  of  the  Lamarckian. 
The  slight  changes  which  nearly  every  organ- 
ism exhibits  as  the  effects  of  its  environment 
and  which,  for  Lamarck,  are  the  actual  steps 
in  evolution,  are  as  a  matter  of  fact  just  the 
class  of  changes  in  favor  of  the  inheritance 
of  which  there  is  the  least  evidence.  Any  pe- 
culiarity that  an  animal  exhibits  and  that  is 
not  an  inheritance,  but  is  the  result  of  an  in- 
dividual change  due  either  to  an  alteration  of 
habit  or  to  the  direct  influence  of  the  envi- 
ronment, is  called  an  acquired  character ;  and 
the  assumption  that  acquired  characters  are 


104      BIOLOGY  AND  SOCIAL  PROBLEMS 

inherited  is  a  most  doubtful  biological  propo- 
sition. 

The  clarification  of  this  whole  matter,  and 
the  present  attitude  of  the  majority  of  biolo- 
gists toward  it,  are  the  results  chiefly  of  Weis- 
mann's  work.  Weismann  pointed  out  very 
clearly  that  the  multitude  of  cells  that  arose 
by  the  division  of  the  egg  cell,  and  that 
eventually  constituted  the  body  of  an  adult 
animal,  could  be  grouped  into  two  sets,  the 
somatic  cells  and  the  germ  cells.  The  somatic 
cells  are  represented  by  those  cells  that  give 
rise  to  skin,  bone,  muscle,  nerve,  and  other 
non-reproductive  tissues.  They  constitute  the 
great  mass  of  the  body  and  carry  on  all  its 
functions  except  that  of  sexual  reproduction. 
The  germ  cells  are  those  that  give  rise  to 
sperm  cells  or  egg  cells,  and  that  are  there- 
fore primarily  concerned  with  reproduction. 
Both  the  germ  cells  and  the  somatic  cells  in 
any  individuals  are  descendants  of  the  egg 
cell  from  which  that  individual  arose,  but  they 
are  not  derived  one  from  the  other.  Germ 
cells  are  cells  that  are  differentiated  directly 
from  certain  of  the  unmodified  cells  that  re- 
sult from  the  division  of  the  egg  cell  and 
never  from  cells  that  begin  to  show  a  tend- 


EVOLUTION  105 

ency  to  become  somatic  cells.  In  a  similar 
way,  somatic  cells  are  never  derived  from  cells 
which  have  begun  to  assume  the  character  of 
germ  cells,  but  are  also  directly  derived  from 
the  segmented  egg.  The  two  classes  of  cells 
are  thus  fundamentally  distinct,  and  it  is  not 
inappropriate  to  describe  the  body  of  one  of 
the  higher  animals  as  composed  of  an  enor- 
mous aggregation  of  somatic  cells  in  which  is 

oo      o 

harbored  and  protected  a  certain  number  of 
germ  cells. 

What  has  been  defined  as  acquired  charac- 
ters, namely,  those  changes  which  are  not  the 
products  of  inheritance,  but  which  are  the  di- 
rect results  of  some  change  in  the  environ- 
ment or  in  the  activities  of  an  animal,  are 
necessarily  alterations  in  its  somatic  cells.  The 
change  in  a  muscle  in  consequence  of  a  new 
form  of  exercise  is  a  change  in  somatic  cells ; 
the  alteration  that  the  skin  exhibits  under  a 
new  exposure  is  of  the  same  kind ;  the  change 
in  the  nervous  mechanism  by  which  a  new 
habit  is  established  is  also  somatic.  If  acquired 
characters,  then,  are  modifications  in  the  so- 
matic cells,  and  these  cells  are  distinct  from 
the  germ  cells,  it  is  difficult  to  see  how  a  change 
which  may  affect  a  group  of  somatic  cells, 


106     BIOLOGY  AND  SOCIAL  PROBLEMS 

skin  cells,  for  instance,  can  so  influence  the 
germ  cells  of  the  same  animal  as  to  produce 
the  newly  acquired  trait  in  its  offspring.  That 
the  germ  cells  are  influenced  by  the  somatic 
cells  there  can  be  not  the  least  doubt,  but 
that  this  influence  shall  result  in  repro- 
ducing in  the  somatic  cells  of  the  offspring 
exactly  the  condition  acquired  by  the  cor- 
responding cells  of  the  parents  is  almost  in- 
conceivable. Since  there  is  no  known  means 
either  in  descent  or  otherwise  of  transferring 
the  changes  which  occur  in  the  somatic  cells 
of  an  individual  to  its  own  germ  cells  so  as 
to  insure  that  these  changes  may  be  handed  on 
as  such  to  its  offspring,  Weismann  was  led  to 
suspect  that  acquired  characters  were  not  in- 
herited, and  that,  therefore,  the  Lamarckian 
hypothesis,  natural  and  simple  as  it  appeared 
on  the  surface,  was  untenable. 

The  experimental  evidence  that  has  been 
gathered  concerning  this  question  has  been 
largely  in  support  of  Weismann's  contention. 
One  of  the  first  lines  of  experimental  work  to 
be  instituted  in  this  direction  was  that  on  mu- 
tilations. The  tails  of  rats  and  mice  were  cut 
off  generation  after  generation  with  the  inten- 
tion of  discovering  whether  this  process  tended 


EVOLUTION  107 

to  induce  a  shorter  tail  in  the  descendants. 
All  such  experiments  yielded  absolutely  nega- 
tive results  and  fell  in  line  with  what  was 
known  of  the  oft-repeated  mutilations  of  the 
human  body  as,  for  instance,  in  the  Jewish 
practice  of  circumcision.  From  observations  of 
this  kind  it  was  soon  concluded  that  such  ac- 
quired characters  as  mutilations  were  not  in- 
herited. 

The  effects  of  changes  of  temperature  on 
one  generation  and  their  inheritance  by  the 
next  were  likewise  tested.  Certain  butterflies, 
when  in  the  pupal  stage,  were  subjected  to  ab- 
normal temperatures  and  in  consequence  the 
wing-markings  were  much  modified.  These 
changes  were  shown  to  be  inherited  by  their 
descendants.  But  it  was  pointed  out  with  cor- 
rectness that  the  pupal  insects  on  which  the 
abnormal  temperatures  acted  carried  in  their 
bodies,  almost  fully  formed,  the  germ  cells  for 
the  next  generation,  and  that  these  germ  cells 
were  just  as  much  open  to  the  effects  of  the 
change  in  temperature  as  the  somatic  cells  of 
the  parent  were.  Hence  such  instances  were 
set  aside  as  not  crucial. 

The  same  is  true  of  the  effect  of  light  in 
producing  pigmented  individuals  of  the  sala- 


108      BIOLOGY  AND  SOCIAL  PROBLEMS 

mander  Proteus.  This  inhabitant  of  caves 
when  reared  in  its  natural  dark  surroundings 
is  without  much  pigment  and  consequently  of 
a  delicate  flesh-tint.  When  reared  in  the  light, 
it  develops  a  well-marked  dark  coloration.  The 
newly  born  descendants  of  such  dark  parents 
emerge  at  once  as  dark  individuals  as  though 
this  peculiarity  had  been  transmitted  to  them 
from  their  parents.  But  as  Kammerer,  who 
has  recently  studied  this  problem,  has  pointed 
out,  the  body  of  Proteus  is  so  translucent  that 
the  light  can  reach  and  affect  its  germ  cells 
and  thereby  influence  the  next  generation,  as 
well  as  modify  its  somatic  cells.  In  conse- 
quence of  this  semi-transparency  light  can 
affect  the  interior  of  Proteus  as  a  temperature 
change  can  that  of  most  lower  animals.  Possi- 
bly in  some  such  way  as  this  are  to  be  explained 
Kammerer's  later  results  on  the  spotted  sala- 
mander of  Europe.  This  animal  becomes 
lighter  in  color  when  reared  on  a  light  clay 
background  and  darker  when  reared  on  a  dark- 
earth  background,  and  the  descendants  of  two 
such  stocks  show  at  once  the  parental  acqui- 
sitions. Kammerer  regards  this  as  a  conclusive 
case  of  the  inheritance  of  acquired  characters, 
but  before  it  can  be  so  accepted,  it  must  be 


EVOLUTION  109 

shown  beyond  the  vestige  of  doubt  that  the 
germ  cells  are  not  affected  in  some  such  way 
as  that  assumed  for  Proteus,  and  the  observa- 
tions themselves  should  be  confirmed  by  other 
workers.  These  experiments,  like  those  on  mu- 
tilations, though  they  have  yielded  interesting 
material,  have  not  yet  produced  indubitable 
evidence  of  the  inheritance  of  acquired  char- 
acters. 

If  such  characters  were  really  inherited,  it 
ought  not  to  be  difficult  to  show  that  the  so- 
matic cells  of  a  given  animal  can  exert  a  con- 
siderable influence  on  the  germ  cells  contained 
within  the  body.  Experimental  attempts  in  this 
direction  have  been  made  by  the  transplanta- 
tion of  ovaries.  Magnus  removed  the  ovaries 
from  a  black  rabbit  and  grafted  into  their  places 
those  from  an  albino  rabbit.  The  black  rabbit 
was  then  paired  with  a  white  male  and  gave 
birth  to  two  offspring,  one  white  and  the  other 
black.  A  similar  experiment  was  then  tried 
by  Guthrie  on  the  hen  and  with  similar  re- 
sults. Both  these  experiments  were,  however, 
inconclusive,  for  the  stock  on  which  the  tests 
were  made  was  not  well  known  and  its  pu- 
rity, therefore,  was  not  established.  Castle  and 
Phillips,  in  1911,  reported  similar  experiments 


110     BIOLOGY  AND  SOCIAL  PROBLEMS 

on  pedigreed  guinea-pigs  and  with  results  of  a 
more  conclusive  character.  I  shall  state  these 
in  Castle's  own  words :  "  A  female  albino 
guinea-pig,  just  attaining  sexual  maturity,  was 
by  an  operation  deprived  of  its  ovaries,  and 
instead  of  the  removed  ovaries  there  were  in- 
troduced into  her  body  the  ovaries  of  a  young 
black  female  guinea-pig,  not  yet  sexually  ma- 
ture, aged  about  three  weeks.  The  grafted 
animal  was  now  mated  with  a  male  albino 
guinea-pig.  From  numerous  experiments  with 
albino  guinea-pigs  it  may  be  stated  emphatic- 
ally that  normal  albinos  mated  together,  with- 
out exception,  produce  only  albino  young,  and 
the  presumption  is  strong,  therefore,  that  had 
this  female  not  been  operated  on  she  would 
have  done  the  same.  She  produced,  however, 
by  the  albino  male  three  litters  of  young  which 
together  consisted  of  six  individuals."  "  The 
first  litter  .  .  .  was  produced  about  six  months 
after  the  operation,  the  last  one  about  a  year. 
The  transplanted  ovarian  tissue  must  have  re- 
mained in  its  new  environment,  therefore,  from 
four  to  ten  months  before  the  eggs  attained 
full  growth  and  were  discharged,  ample  time, 
it  would  seem,  for  the  influence  of  the  foreign 
body  upon  the  inheritance  to  show  itself  were 


EVOLUTION  111 

such  influence  possible."  All  the  young  were 
black.  The  white  body  of  the  foster  mother, 
then,  had  no  influence  on  the  transplanted 
egg  cells,  thus  demonstrating  in  this  respect 
the  independence  of  germ  cells  and  somatic 
cells  in  one  individual.  (Plate  IV.) 

The  evidence  from  experiments  on  the  in- 
heritance of  mutilations,  as  well  as  on  the 
transmission  of  changes  of  a  more  normal 
kind,  and  from  observations  on  the  effects 
of  a  foster  parent  body  on  transplanted  egg 
cell,  is  thus  unfavorable  to  the  view  that  ac- 
quired characters  are  heritable.  If  such  char- 
acters are  inherited,  it  ought  to  be  easy  to 
demonstrate  the  truth  of  this  proposition, 
but  the  fact  that  there  is  not  a  single  un- 
equivocal case  in  its  favor,  though  the  prop- 
osition has  been  tested  in  many  ways,  is  much 
against  it.  The  adverse  evidence  is  all  nega- 
tive, and  though  conclusive  negative  evidence 
is  most  difficult  to  obtain,  that  which  is  at 
hand  is  so  strongly  negative  that,  inviting  as 
the  proposition  is,  the  inheritance  of  acquired 
characters  cannot  be  said  to  be  supported  by  t 
present-day  biological  observation. 

That  man  is  not  an  exception  to  the  rule 
just  laid  down  seems  at  first  sight  startling, 


112      BIOLOGY  AND  SOCIAL  PROBLEMS 

if  not  absurd.  To  maintain  that  what  we  ac- 
quire during  life  has  no  effect  upon  our  de- 
scendants seems  to  be  flying  into  the  face  of 
observed  fact  and,  if  true,  to  remove  one  of 
the  main  springs  that  activate  social  progress. 
That  the  right  or  wrong  course  of  the  par- 
ent's life  flows  on  more  or  less  through  that 
of  the  child  is  one  of  the  fundamental  beliefs 
of  human  nature  and  has  long  been  held  out 
by  moralists  as  an  incentive  to  upright  living. 
This  doctrine,  however,  seems  to  be  in  direct 
opposition  to  the  attitude  of  most  modern 
biologists  toward  the  question  of  the  inherit- 
ance of  acquired  characters.  But  the  contrast 
thus  set  up,  when  carefully  scrutinized,  is  found 
to  be  not  a  contrast,  after  all,  but  rather  a 
confusion  due  to  the  complexities  of  human 
inheritance. 

The  transmission  of  traits  from  parent  to 
offspring,  as  we  see  it  exhibited  in  guinea-pigs 
and  other  organisms,  is  so  like  the  transmis- 
sion of  property  from  parent  to  child  in  every- 
day life  that  we  call  both  by  the  same  name, 
inheritance.  But  we  must  never  forget  that 
the  inheritance  of  property  is  the  original 
process  and  that  the  other  is  but  a  figure  of 
speech.  That  there  are  fundamental  differ- 


EVOLUTION  113 

ences  between  the  two  cannot  for  a  moment 
be  doubted.  In  the  inheritance  of  property 
the  same  article  is  passed  on  from  parent  to 
child,  but  in  -what  we  call  inheritance  in  sexual 
reproduction,  the  part  inherited  is  not  passed 
on  from  the  parent  through  the  egg  to  the 
offspring,  but  only  a  tendency  or  activity  rep- 
resenting such  a  part.  Moreover,  as  we  have 
already  seen,  such  tendencies  do  not  even 
emanate  from  the  parental  part  in  question, 
but  come  directly  from  the  racial  store  con- 
tained in  the  germ  cells.  Thus  it  must  be  evi- 
dent that  the  inheritance  of  property  and  the 
inheritance  of  traits  are  very  different  proc- 
esses, and,  since  both  occur  in  the  human  be- 
ing, it  is  important  that,  though  we  use  the 
same  name  with  which  to  designate  them,  we 
keep  the  two  processes  clearly  separated  in 
our  minds. 

That  the  inheritance  of  property  in  the 
ordinary  sense  of  the  word  is  a  most  significant 
factor  in  human  affairs  needs  no  comment.  It 
is,  however,  a  practice  that  few  other  animals 
have  adopted.  Ants  continue  to  inhabit  the 
same  hill  generation  after  generation  and  thus 
inherit  and  enjoy  the  results  of  their  ancestors' 
labors.  Other  social  animals  may  afford  similar 


114     BIOLOGY  AND  SOCIAL  PROBLEMS 

examples,  but  the  instance  par  excellence  of 
the  inheritance  of  property  is  to  be  found 
in  the  human  species.  As  a  social  proposition 
this  practice  has  its  advantages,  though  its 
effect  on  many  individuals  in  removing  their 
incentive  to  normal  activity  shows  that  the 
curse  of  the  Nibelungs'  hoard  is  more  than  a 
poetic  fancy. 

But  is  everything  that  we  inherit  from  our 
parents  either  an  object  handed  down  to  us 
in  a  physical  sense  or  a  tendency  or  other  in- 
direct influence  transmitted  to  us  through  the 
egg  ?  Probably  not !  A  large  part,  perhaps 
the  larger  part,  of  what  we  are  accustomed  to 
say  makes  up  our  lives  is  obtained  neither  as  an 
inherited  object  nor  as  a  transmitted  tendency, 
but  has  reached  us  in  a  somewhat  different 
way.  What  comes  to  us  over  this  third  route 
maybe  put  briefly  as  our  heritable  intelligence. 
As  I  pointed  out  in  the  first  lecture,  the  mind 
of  the  young  child  is  an  unwritten  page  on 
which  the  environment,  acting  through  the 
sense  organs,  inscribes  the  story  of  life.  Much 
of  the  sensory  inflow  is  controlled  and  directed 
by  the  parent,  and  thus  in  the  early  stages 
of  life  he  can  exert  a  most  profound  influence 
on  the  personality  of  the  child.  With  the 


EVOLUTION  115 

awakening  of  the  emotions  and  the  develop- 
ment of  attachments,  the  parent  usually  comes 
to  be  an  example  to  the  child,  and  imitation 
adds  greatly  to  the  obvious  similarity  of  the 
two  minds.  With  the  development  of  mental 
independence  on  the  part  of  the  offspring, 
the  parental  attitudes  and  acts  may,  however, 
prove  repugnant  to  the  maturing  individual 
and  lead  to  some  courses  of  action  directly 
the  opposite  of  those  of  the  ancestor.  Thus, 
a  dissimilarity,  which,  however,  may  rest  upon 
a  more  deep-seated  agreement,  may  make  its 
appearance ;  the  children  of  the  over-religious 
may  seek  irreligion ;  those  of  the  drunkard, 
total  abstinence.  Into  the  quickening  mind 
of  the  developing  individual,  with  its  growing 
knowledge,  its  expanding  sympathies,  and  its 
increasing  capacity  for  action,  the  inheritance 
of  the  race  is  poured ;  knowledge  representing 
the  past  experience  of  mankind  with  all  the 
power  it  gives,  the  imagery  of  times  gone  by 
with  its  capacity  to  awaken  the  emotions,  in 
short  the  total  record  of  human  effort  in  so 
far  as  it  is  preserved.  This  race  inheritance 
comes  to  us  from  human  memory,  from  the 
written  page,  and  from  a  thousand  other 
sources.  It  meets  us  on  every  side,  but  it  is 


116      BIOLOGY  AND  SOCIAL  PROBLEMS 

the  special  office  of  our  educational  institu- 
tions to  preserve  it  and  hand  it  on.  From  the 
child  at  the  knee  to  the  university  student, 
all  are  learning  from  the  same  general  source. 
Thus  the  process  of  acquisition  goes  on,  and 
as  a  result  we  expect  an  individual  not  only 
with  a  well-stored  mind,  but  capable  of  using 
his  mental  equipment  in  the  performance  of 
serviceable  acts,  the  broadening  of  sympathies, 
and  the  discovery  of  new  truths. 

Such  a  result  is  the  exclusive  outcome  of 
neither  one  nor  the  other  of  the  two  methods 
of  inheritance  that  we  have  described.  If  we 
designate  that  through  the  germ  cell  as  organic 
and  that  by  direct  transfer  as  social  inherit- 
ance, we  can  say  that  our  intellectual  outfit 
comes  to  us  more  in  the  nature  of  a  social 
contribution  than  of  an  organic  one.  The 
content  of  the  mind  is  not  congenital ;  it  is  a 
vast  mass  of  subsequent  acquisition.  It  is  in 
every  sense  a  veritable  body  of  acquired  char- 
acters. It  is,  therefore,  not  to  be  expected  that 
it  will  ever  become  hereditary.  The  rudiments 
of  learning  must  be  acquired  by  all ;  even  the 
genius  must  begin  with  the  alphabet;  and 
there  is  no  reason  to  suppose  that  the  time 
will  ever  come  when  a  pedigreed  birth  certif- 


EVOLUTION  117 

icate  will  take  the  place  of  a  college  entrance 
examination.  As  educators  our  task  is  limited 
only  by  the  supply  of  human  beings.  The 
automobile  may  drive  out  the  horse,  but  the 
educator,  whatever  the  community  may  think 
of  him,  has  come  to  stay. 

If,  however,  the  content  of  the  mind  is  of 
the  nature  of  acquired  traits  and  hence  not 
heritable,  the  mental  machinery  by  which  this 
content  is  handled  is,  in  part  at  least,  heredi- 
tary. The  inheritances  of  feeble-mindedness, 
insanity,  and  other  defects,  as  well  as  of  favor- 
able traits,  such  as  predisposition  to  music 
and  so  forth,  are  too  well  established  as  ger- 
minal features  to  admit  of  dispute.  They  re- 
semble a  more  stable  background  on  which 
our  somewhat  plastic  natures  rest,  and,  though 
their  well-being  is  essential  to  our  success, 
they  of  themselves  afford  only  that  founda- 
tion on  which  such  a  success  may  be  built. 
Thus  our  personality  springs  from  a  heredi- 
tary soil,  but  the  direction  of  its  growth  is 
more  a  matter  of  environment  than  of  ger- 
minal determination.  Although  the  Lamarck- 
ian  hypothesis  seems  to  have  no  assured  place 
as  a  real  factor  in  the  process  of  organic  evo- 
lution, if  we  widen  our  conception  of  this 


118      BIOLOGY  AND  SOCIAL  PROBLEMS 

process  to  include  the  mental  growth  of  man, 
Lamarckism  affords  an  accurate  statement  of 
the  way  by  which  much  of  our  mental  equip- 
ment has  come  to  us,  though  this  statement, 
as  compared  with  that  advanced  by  Lamarck 
and  his  followers,  is  figurative  rather  than 
real.  What  we  do  not  get  by  social  inherit- 
ance, however,  we  obtain  by  the  strictest  kind 
of  organic  transmission.  Thus  our  personal- 
ity is  in  part  an  organic  and  in  part  a  social 
heritage. 

With  the  evidence  so  preponderatingly 
against  Lamarckism  as  an  effective  factor  in 
organic  evolution,  there  is  left  as  a  guiding 
principle  for  the  transmutationists  little  more 
than  Darwin's  theory  of  natural  selection. 
This  theory  is  so  well  known  in  its  general 
outlines  as  to  require  no  special  exposition. 
Every  species,  according  to  Darwin,  produces 
many  more  offspring  than  can  possibly  reach 
maturity.  These  offspring  all  differ  somewhat 
one  from  another.  In  consequence,  at  any  pe- 
riod of  stress  those  individuals  whose  differ- 
ences lie  in  the  directions  favorable  for  life 
are  more  likely  to  survive  than  those  that  ex- 
hibit unfavorable  differences.  Thus  the  more 
favored  individuals  tend  to  be  preserved  and 


EVOLUTION  119 

to  become  the  progenitors  of  a  new  stock 
bearing  the  favorable  traits. 

The  individual  differences  which  Darwin  be- 
lieved to  afford  a  basis  for  this  process  are 
not  the  characters  acquired  during  life,  but 
are  those  features  with  which  the  young  or- 
ganism is  born.  These  differences  are  germinal 
in  their  origin,  and  therefore  may  be  handed 
on ;  in  other  words,  Darwin's  theory  avoids 
the  difficulty  of  the  inheritance  of  acquired 
characters  and  is  based  upon  what  is  known 
to  be  heritable  differences. 

That  natural  selection  is  a  process  that  oc- 
curs in  nature  seems  to  be  beyond  dispute. 
A  single  instance  may  suffice  to  show  this. 
After  a  severe  winter  storm  in  Providence, 
Ehode  Island,  on  February  1,  1898,  many  of 
the  English  sparrows  of  that  region  were  found 
to  be  much  spent  and  exhausted.  Of  these 
birds,  one  hundred  and  thirty-six  were  col- 
lected and  brought  within  doors,  and  of  this 
number  seventy-two  revived  and  sixty-four 
died.  A  close  comparison  of  these  two  sets 
disclosed  the  fact  that  the  birds  that  died 
were  less  near  the  normal  than  those  that  sur- 
vived, showing  that,  for  instance,  a  heavy  body 
with  small  wings  or  a  light  body  with  large 


120      BIOLOGY  AND  SOCIAL  PROBLEMS 

wings  was  less  advantageous  under  stress  of 
circumstances  than  a  body  of  average  weight 
carrying  wings  of  average  extent.  In  this  in- 
stance, then,  natural  selection  could  be  said 
to  take  place  in  that  extreme  inclemency  tended 
to  eliminate  the  less  fit.  Other  instances  of  a 
like  kind  have  shown  that  this  process  is  of 
common  occurrence  in  nature. 

But  though  we  may  feel  confident  that  nat- 
ural selection  is  of  actual  occurrence,  it  is  by 
no  means  certain  that  it  is  of  first  importance. 
Numerous  serious  and  valid  objections  to  it 
have  been  raised  from  time  to  time.  The  most 
telling  of  these  is  the  difficulty  experienced  in 
understanding  how  in  a  given  species  new 
characters  can  get  a  foothold.  The  slight  in- 
dividual differences  that  Darwin  assumed  to 
be  the  beginnings  of  new  traits  are  altogether 
too  insignificant  to  be  of  selectional  value,  and 
hence  it  seems  impossible  that  the  initial  step 
in  the  origin  of  such  a  trait  could  be  taken 
by  natural  selection.  This  objection  has  been 
fairly  met  by  the  mutation  theory  of  De  Vries. 
According  to  this  theory  the  differences  ef- 
fective in  evolution  are  not  the  small  individ- 
ual variations,  such  as  were  considered  so 
important  by  Darwin,  but  the  considerable 


EVOLUTION  121 

sudden  changes,  or  mutations  as  they  have 
been  called,  and  which,  since  the  revival  of 
Mendel's  work,  have  been  found  to  occur  in 
most  animals  and  plants.  These  differences, 
like  Minerva,  are  born  in  their  fullness,  and 
selection  may  act  upon  them  at  once.  Thus  it 
is  well  known  that  from  time  to  time  albino 
individuals  appear  in  stocks  of  wild  as  well  as 
of  domesticated  animals.  Such  an  appearance 
is  a  mutation,  and  in  the  case  of  wild  animals 
living  in  a  district  where  dark  coloration  is  of 
protective  importance,  the  individuals  bearing 
this  trait  would  probably  be  quickly  exter- 
minated ;  but  in  an  environment  like  the 
polar  regions  where  whiteness  is  an  advan- 
tage, such  individuals  might  well  be  preserved 
and  in  the  end  give  rise  to  a  white  stock. 

Such  hypothetical  cases  show  us  how  nat- 
ural selection  may  take  place,  and  yet  we  have 
reason  to  suspect  that  the  process  itself  is  not 
so  simple.  Selection  is  supposed  to  act  on  what 
Weismann  might  call  the  somatic  qualities  of 
individuals,  coat-color,  size  of  body,  strength 
of  muscle,  and  so  forth,  and  it  is  assumed  that 
these  traits,  since  they  are  germinal  in  origin, 
would  be  reproduced  in  the  offspring.  But,  as 
we  saw  from  the  breeding  experiments  with 


122      BIOLOGY  AND  SOCIAL  PROBLEMS 

the  black  and  white  guinea-pigs  already  al- 
luded to,  we  may  have  two  individuals  with 
indistinguishable  exteriors  and  yet  with  very 
different  germinal  possibilities.  One  stock  of 
black  guinea-pigs,  depending  upon  its  ances- 
try, is  able  to  produce  nothing  but  black  de- 
scendants, and  another  stock  of  black  indi- 
viduals, indistinguishable  externally  from  the 
first  but  differing  from  it  in  its  ancestry,  can 
bring  forth  white  offspring  as  well  as  black. 
In  the  preservation  of  black  individuals,  nat- 
ural selection  would  act  the  same  in  the  two 
stocks,  but  one  stock  would  be  more  effective 
than  the  other  in  establishing  a  black  race. 
Thus  germinal  composition  may  be  a  factor  of 
no  small  importance  in  limiting  the  effective- 
ness of  natural  selection,  a  process  which  is 
of  undoubted  significance  in  nature,  but  which 
may  be  much  more  restricted  in  its  applica- 
tion and  effectiveness  than  its  advocates  have 
suspected. 

That  natural  selection  influences  man  as  it 
does  other  organisms  is  an  undoubted  fact. 
Every  epidemic  that  carries  off  human  beings 
acts  selectively,  and  if  it  affects  individuals  in 
early  life  and  before  the  period  of  reproduc- 
tive activity,  it  may  have  great  importance 


EVOLUTION  123 

from  the  standpoint  of  natural  selection.  Un- 
doubtedly the  differences  in  the  immunity  to 
various  diseases  characteristic  of  different  hu- 
man races  are  to  be  attributed  to  this  kind  of 
influence.  But  that  natural  selection  has  been 
the  main  driving  force  in  the  evolution  of 
man  is  no  more  to  be  admitted  than  it  is  in  re- 
spect to  the  other  organisms.  Natural  selection 
seems  to  be  a  real  but  subordinate  factor  in 
organic  evolution,  the  mechanism  of  which  is 
still  to  be  discovered. 

In  man  much  of  his  social  practice  tends  to 
reduce  rather  than  to  preserve  the  efficiency 
of  natural  selection.  In  ancient  times  and  in 
primitive  races  to-day  the  malformed  or  other- 
wise defective  infant  is  often  destroyed,  thus 
anticipating  what  is  likely  to  happen  later 
through  purely  natural  causes.  With  the 
growth  in  our  civilization  of  the  sense  of  value 
in  human  life,  these  practices  have  become 
mostly  illegal  and  have  been  largely  sup- 
pressed. As  a  result  we  have  developed  a  large 
body  of  institutions  for  the  care  of  our  defec- 
tives, institutions  supported  by  a  strong  pub- 
lic opinion.  Such  social  undertakings  are  ift 
direct  opposition  to  the  workings  of  natural 
selection.  They  are  a  drain  on  the  social  body, 


124      BIOLOGY  AND  SOCIAL  PROBLEMS 

but  they  are  justifiable  for  the  reason  that  they 
inculcate  a  respect  for  life  and  a  public  habit 
of  humane  treatment  of  unfortunates,  charac- 
teristics without  which  no  race  can  afford  to 
be.  But  they  are  not  unqualified  blessings. 
And  when  we  examine  them  from  the  stand- 
point of  evolution,  they  seem  to  contain  an 
element  of  no  small  danger  to  the  state.  While 
it  is  avowedly  advantageous  to  the  community 
as  a  whole  to  treat  with  all  reasonable  care  its 
defective  members,  it  is  quite  clear  that  this 
class,  so  far  as  its  traits  are  hereditary,  is  not 
the  class  from  which  the  future  of  society 
should  be  recruited.  It  seems  proper,  therefore, 
since  our  social  institutions  have  counteracted 
to  a  certain  degree  the  effects  of  natural  selec- 
tion and  have  thus  brought  about  conditions 
that  are  unduly  burdensome  to  the  common- 
wealth, if  not  really  menacing  to  the  welfare 
of  society  itself,  that  the  state  should  regulate 
the  reproductive  activity  of  certain  classes  of 
defective  individuals.  This  can  be  done  in  two 
ways  :  first,  by  educating  all  persons  to  a  sense 
of  their  social  responsibilities  in  reproduction 
and  then  relying  upon  them  to  act  in  accord- 
ance with  this  training;  and,  secondly,  where 
such  education  is  impossible,  by  sterilizing  the 


EVOLUTION  125 

individual  through  means  that  are  effective, 
but  that  are  as  little  disturbing  to  his  person- 
ality as  possible.  By  these  methods  reasonable 
self-restraint  can  be  brought  into  play  or  a 
final  barrier  set  in  the  way  of  the  irresponsi- 
ble. That  so  radical  a  course  as  the  latter  is 
justifiable  will  be  apparent  to  any  one  who 
follows  the  history  of  many  of  the  charges 
in  our  public  institutions  for  the  feeble- 
minded. 

In  the  programme  of  the  eugenicists, 
heartily  agree  with  that  portion  which  is  di- 
rected toward  the  complete  elimination  of  re- 
production by  the  irresponsible  defective.  Such 
a  step  is  merely  a  reinstitution  in  modern  hu- 
man evolution  of  a  rapidly  disappearing  phase 
of  natural  selection.  When,  however,  the  ac- 
tivity of  eugenics  is  shifted  from  that  of  the 
elimination  of  the  most  undesirable  to  exclu- 
sive reproduction  by  the  most  desirable,  I  find 
it  difficult  to  settle  in  my  own  mind  how  this 
high-grade  stock  is  to  be  selected.  My  neigh- 
bors are  charitably  inclined,  but  some  of  them, 
I  am  sure,  would  give  what  seemed  to  them 
good  reasons  for  not  having  my  particular 
personality  repeated  in  the  future,  and  yet, 
with  all  due  respect  to  the  welfare  of  society, 


126      BIOLOGY  AND  SOCIAL  PROBLEMS 

I  confess  to  a  slight  measure  of  feeling  that 
I  be  allowed  some  individual  freedom  in  this 
matter. 

And  this  brings  me  to  another  aspect  of 
the  social  evolution  in  man.  We  have  seen 
how  immensely  powerful  and  compelling  the 
forces  of  organic  inheritance  are,  but  we  have 
also  seen  that  what  we  call  ourselves  is  a 
growth  built  up  in  our  nervous  organization 
in  part  directly  by  daily  experience  and  in 
part  indirectly  by  what  I  have  called  social 
inheritance.  The  personality  thus  developed, 
though  it  must  depend  upon  a  certain  or- 
ganically inherited  soil  and  cannot  rightly 
flourish  unless  this  is  wholesome,  is  in  itself 
no  whit  less  important  a  factor  in  the  evolu- 
tion of  man  than  that  of  inheritance  through 
the  substance  of  the  egg.  Memory  and  above 
all  the  ability  to  act  voluntarily  are  most  sig- 
nificant factors  in  our  daily  affairs.  Without 
them  the  fabric  of  human  society  would  never 
have  come  into  existence.  Voluntary  action  is 
a  basic  fact  upon  which  all  social  responsibil- 
ity rests.  It  makes  a  code  of  morals  effective. 
By  education  this  capacity  can  be  greatly 
improved  and  set  forward  and  no  small  part 
of  human  progress  has  depended  upon  this 


EVOLUTION  127 

fact.  Improvement  of  this  kind  through  a 
favorable  environment,  educational  or  other- 
wise, can  transform  a  being  whose  hereditary 
outlook  is  poor  into  one  whose  service  to  so- 
ciety may  be  great,  for  a  new  discovery,  a  sub- 
lime idea,  or  even  a  kind  act  has  its  place  in 
the  evolution  of  man  as  much  as  a  hereditary 
trait.  One  comes  to  us  by  social  inheritance, 
the  other  by  organic.  These  two  processes, 
the  one  depending  upon  the  nervous  system, 
the  other  upon  the  reproductive  mechanism, 
though  treated  more  or  less  separately  in  these 
lectures,  are  in  reality  inextricably  interwoven 
in  our  natures.  For  a  right  understanding  and 
control  of  our  social  acts,  it  is  necessary  to 
know  the  extent  to  which  each  factor  underlies 
them.  This  determined,  the  organic  constitu- 
ent may  be  modified,  improved,  or  otherwise 
controlled  through  the  principles  of  genetics 
as  applied  to  the  reproductive  processes,  and 
the  social  constituent  may  similarly  be  dealt 
with  through  environmental  changes,  train- 
ing, and  education  in  their  broadest  sense. 
These  two  factors  thus  mutually  interrelated 
are  the  fundamental  biological  elements  that 
underlie  our  social  structure. 

In  dealing  with  these  elements  in  the  present 


138      BIOLOGY  AND  SOCIAL  PROBLEMS 

lectures,  I  have  repeatedly  taken  occasion  to 
point  out  their  relation  to  the  materials  of  the 
body.  Organic  inheritance  is  dependent  upon 
the  minute  amount  of  these  materials  in  the 
fertilized  egg,  perhaps  even  upon  those  in  the 
chromosomes.  By  means  of  these  substances 
and  in  no  other  way  are  the  organically  herit- 
able traits  handed  on  from  parent  to  child. 
Social  inheritance  is  dependent  upon  the  ap- 
proximate cubic  inch  of  nervous  protoplasm 
contained  in  our  cerebral  cortex  and  serving 
as  a  means  for  our  conscious  operations.  When 
this  is  removed,  diseased,  or  temporarily  dis- 
turbed, as  by  poisons  and  the  like,  the  whole 
personality  is  shaken  to  the  core  or  even  van- 
ishes. From  a  variety  of  directions,  we  have 
as  strong  reasons  for  believing  that  that  whole 
aggregate  of  nervous  states  that  we  recognize 
as  our  inmost  selves  is  as  essentially  associated 
with  the  cortical  protoplasm  as  organic  inher- 
itance is  with  the  materials  of  the  egg.  In 
neither  case  do  we  understand  much  of  the 
process.  That  is  a  subject  for  future  investi- 
gation, but  research  has  gone  far  enough  to 
show  that  these  two  classes  of  operations,  the 
most  wonderful,  perhaps,  that  go  on  in  the 
body,  are  bound  up  indissolubly  with  their 


EVOLUTION  129 

several  kinds  of  protoplasm  and  occur  under 
no  other  circumstances. 

As  we  know  that  the  materials  of  the  egg 
cells  and  of  the  cortex  are  undergoing  contin- 
ual disintegration  and  that  the  loss  that  they 
thus  suffer  is  regularly  made  good  by  the  ap- 
propriation of  new  material  which  comes  di- 
rectly or  indirectly  from  the  inorganic  sur- 
roundings, the  inference  is  that  our  most 
profound  activities  are  of  a  purely  materialis- 
tic nature.  And  this  conclusion  seems  to  me 
to  be  entirely  correct.  But  when  we  think  of 
material,  we  are  prone  to  regard  only  its  inor- 
ganic aspects  and  we  often  forget  of  what  it 
is  capable  when  organized  into  living  sub- 
stance ;  in  doing  this  we  miss  completely  its 
most  profound  characteristics.  In  this  respect 
the  side  of  approach  is  most  important.  It 
would  be  an  interesting  speculation  to  inquire 
what  would  be  our  present  outlook  on  nature 
had  science  made  its  first  fundamental  discov- 
eries in  the  organic  instead  of  in  the  inorganic. 
I  am  sure  that  that  outlook  would  have  been 
different  from  what  it  is  now,  but  I  am  also 
equally  sure  that  that  difference,  large  as  it 
might  seem  to  some  of  us  at  present,  would 
prove  in  the  end  to  be  temporary  and  illusory, 


130     BIOLOGY  AND  SOCIAL  PROBLEMS 

for,  from  whichever  side  of  the  problem  we 
make  the  approach,  there  is  but  one  goal. 

Of  the  nature  of  living  substance  we  are 
only  just  beginning  to  get  a  dim  appreciation, 
but  when  this  appreciation  grows  to  some- 
thing of  an  understanding,  we  shall  feel,  I  be- 
lieve, no  more  hesitancy  in  abandoning  our  old 
view  of  the  separateness  of  self  and  body  and 
accepting  that  of  their  common  nature  than  in 
the  past  our  race  had  in  giving  up  Dante's  para- 
dise and  its  ten  heavens  for  the  depths  of  blue 
above  us.  Organized  living  material,  as  we 
meet  it  in  the  cerebral  cortex,  is  so  strictly  a 
part  of  the  universe  and  yet  so  strikingly  dif- 
ferent from  any  other  aggregate  of  material 
known  to  us  that  we  can  look  upon  it  at  pres- 
ent only  with  vague  bewilderment  and  yet  with 
a  hope,  justified  by  the  past  progress  of  sci- 
ence, that  in  time  its  secrets  will  be  gradually 
disclosed  to  us.  With  such  a  view  of  the  poten- 
tialities of  material,  it  is  not  surprising  that 
the  biologist  finds  in  the  study  of  organisms 
a  subject  of  intense  interest  whose  applica- 
tion to  the  problems  of  human  welfare  comes 
to  be  day  by  day  more  apparent  and  intimate. 

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